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NATIONAL HEALTH SERIES 


In order to provide the general public with authoritative books 
on health at low cost, the National Health Council arranged with 
the Funk & Waégnalls Company for the publication of The National 
This series written by leading authorities in the 


Health Series. 
United States. 


Man and the Microbe: How 
Communicable Diseases are Con- 
trolled. By C.-E. A. Winslow, 
Dr. P. H.; Professor of Public 
Health, Yale Schooi of Medicine. 


The Baby’s Health, By Richard 
A. Bolt, M.D., Gr. P. H.; Di- 
rector, Medical Service, Ameri- 
can Child Health Association. 


Personal Hygiene: The Rules 
for Right Living. By Allan J. 
McLaughlin, M.D.; Surgeon, 
United States Public Health 
Service. 


Community Health: How to 
Obtain and Preserve It. By D. 
B. Armstrong, M.D.; Se.D.; As- 
sistant Secretary, Metropolitan 
Life Insurance Company. 


Cancer: Nature, Diagnosis, and 
Cure. By Francis Carter Wood, 
M.D.; Director, Institute for 
Cancer Research, Columbia Uni- 
versity. 


The Human Machine: How 
Your Body Functions. By W. H. 
Howell, Ph.D., M.D., LL.D., 
Se.D.; Associate Director, School 
of Hygiene and Public Health, 
Johns Hopkins University. 


The Young Child’s Health. By 
Henry L. K. Shaw, M.D.; Clin- 
ical Professor, Diseases of Chil- 
dren, Albany Medical College. 


How to care for the health of 
the runabout child from two to 
six years of age. 


The Child in School: Care of 
Its Health. By Thomas D. Wood, 
M.D.; Professor of Physical Edu- 
cation, Teachers College, Colum- 
bia University. 


Tuberculosis: Nature, Treat- 
ment, and Prevention, by Linsly 
R. Williams, M.D.; Managing 
Director, National Twyberculosis 
Association. 


The Quest for Health. Where 
It is and Who can Help Secure 
It. By James A. Tobey, M.S.; 
Former Administrative Secretary, 
National Health Council. 


Love and Marriage: Normal 
Sex Relations; By T. W. Gallo- 
way, Ph.D., Litt.D.; Associate 
Director of Educational Measures, 
American Social Hygiene Asso- 
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Feod for Health’s Sake: What 
to Eat. By Lucy H. Gillett, 
A. M., Superintendent of Nutri- 
tion, Association for Improving 
the Condition of the Poor, New 
York. 


Health of the Worker: How to 
Safeguard It. By Lee K. Frankel, 
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Exercises for Health: By Lenna 
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Venereal Diseases: Their Med- 
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Your Mind and You: Mental 
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giene, Boston. 


Describes how your mind can 
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it can be enlisted as your ally. 


Taking Care of Your Heart. 
By T. Stuart Hart, M.D., Presi- 
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The Expectant Mother: Care of 
Her Health. By R. L. DeNor- 
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Home Care of the Sick: When 
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Adolescence. Educational and 
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The scientific and sociological 
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What Every One Should Know 
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Diabetes and Its Treatment. 
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Care of the Mouth and Teeth. 
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*Cutting Down the Medical Bill. 

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MAN AND 
THE MICROBE 


HOW COMMUNICABLE DISEASES ARE 
CONTROLLED 


BY 
CHARLES-EDWARD AMORY WINSLOW 
Doctor of Public Health; Fellow, A. P. H. A.; 


Professor of Public Health, Yale 
School of Medicine 


THE NATIONAL HEALTH SERIES 


EDITED BY 


THE NATIONAL HEALTH COUNCIL 


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CopyriGcHt, 1924, By 
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Printed in the United States of America 
Published, February, 1924 


Copyright Under the Articles of the Copyright Convention 
of the Pan-American Republics and the 
United States, August 11, 1910 


~ 
— Z ~ 


: 


INTRODUCTION 


THERE are three steps necessary before the benefits 
of scientific medical advance can be available to the 
people at large: First, there must be scientific re- 
search ending in the discovery of facts. This is 
usually accomplished by experimentation on animals 
and observation on man. Second, these discoveries 
must be studied in the prevention or cure of disease. 
This is done by the medical profession throughout 
the world under varying local and climatic condi- 
tions. Third, the knowledge of these facts and the 
methods of their application and utilization must be 
put into popular language and made known and 
available to the people. 

A striking illustration of the above statements will 


“make them clear. In the sixties and seventies of the 


last century Villemin demonstrated by experiments 
on animals (1) that tuberculosis is a contagious and 
therefore a preventable disease, (2) that the virus 
of this disease is present in the sputum and other 
discharges from tuberculous men and animals, (3) 
that the disease is transmitted from man to man and 
from animals to man. A few years later Koch dem- 
onstrated and isolated the living virus in the form 
of a bacillus and proved that it is the sole cause of 
the disease. These discoveries were subjected to 
most critical tests at the hands of medical men and 
it was shown that the bacillus in the sputum and 
other tuberculous excretions is easily destroyed and 
that in this way the spread of the disease might be 
greatly restricted. However, but little was accom- 
plished until intelligent laymen took up the matter 


623242 


INTRODUCTION 


and formed the National Tuberculosis Association in 
1904. Through this and other agencies the public 
has become well informed as to the measures neces- 
sary to restrict it. The result has been a great 
decrease in the number of infections and deaths from 
this disease. 

Similar illustrations might be given with other 
diseases, but these will come out in the text. 

Professor Winslow has rendered the public an 
important service in the preparation of this book. I 
am sure that it will be of great aid to the intelligent 
reader in his efforts to protect himself and those de- 
pendent upon him from infection. 

Victor C, VaucHAN, M.D., LL.D. 


Washington, D. C., January, 1924. 


CONTENTS 


I—PARASITES AND PARASITISM ..... 


The pestilence that walketh in darkness—Primi- 
tive theories of disease—Pasteur—The ubiqui- 
tous microbe—The phenomena of parasitism— 
The carrier—The control of communicable dis- 
ease, 


II—MunIcipAL SANITATION . . 


The care of body discharges—The non of 
sewage—The problem of water-borne disease— 
~The purification of water supplies—Milk supply 
and disease—Sanitary problems of food supplies. 


IlJ—Insects AND DISEASE . 


The filthy fly—Mosquitoes and meee eer he 
conquest of yellow fever—Plagues of the olden 
time. 


IV—Tue Conract-BorneE DISEASES 


Nature and significance of contact infection— 
Isolation and quarantine—The sanitary conscience 
and the aseptic sense. 


V—ARTIFICIAL CONTROL OF IMMUNITY. 


Smallpox and vaccination—The scientific prin- 
ciples of vaccine treatment—The development of 
vaccine prophylaxis—The use of immune sera in 
treatment of disease—The challenge of diphtheria 
—The past and the future, 


17 


32 


43 


52 


MAN AND THE MICROBE 
CHAPTER I 
PARASITES AND PARASITISM 


THE PESTILENCE THAT WALKETH IN DARKNESS 


ye AS the manifold disorders which cripple 
health and efficiency and shorten human life 
there are some whose nature is obvious at a glance. 
Drowning, burning, automobile accidents, sever the 
vital thread with a violence which requires no expla- 
nation. The failings of old age, while their essential 
nature offers problems of deep subtlety to the phy- 
siologist, clearly form a part of a general law which 
must have become familiar even to the untutored 
savage. There is another group of diseases, how- 
ever, whose workings are much more mysterious, the 
group of the plagues, pestilences, and fevers, or as 
we call them to-day, the communicable diseases. 

We have learned so much about these disorders 
during the past half century that it is perhaps difficult 
to realize how deep was the mystery which still 
shrouded them when our grandfathers were young. 
Let us for a moment divest ourselves of this rela- 
tively recent knowledge and consider how puzzling 
the phenomena were which confronted the student of 
these problems only fifty years ago. 

A man wakes up in the morning, young and strong 
and sound. During the day he begins to be conscious 
of a dull uneasiness. He feels tired for no reason. 


1 


7 a MAN AND THE MICROBE 


His head aches. His throat may become sore. Grad- 
ually his discomfort increases. He grows hot and 
feverish. He gives up work, and goes home. He 
can not eat. He decides he is ill and goes to bed. 
He tosses through the night, more and more feverish 
and miserable. In another twelve hours he may be 
so weak that he can scarcely lift his head. In still 
another he may be raving in delirium. 

What has happened, to strike down a man in vigor- 
ous health into a wreck of his former self in a few 
brief hours? 

There is a second characteristic of diseases of this 
class, as remarkable as their sudden and mysterious 
onset. The disorders of old age are generally pro- 
gressive. By medical and hygienic treatment their 
course may be checked, but it is difficult to remedy 
the harm already done. It is true that the fevers fre- 
quently leave behind them ineradicable injuries to 
vital organs. Yet these fevers themselves are essen- 
tially “self-limited” in nature. Irrespective of treat- 
ment of any kind, they run a definite course of days 
or weeks or in some cases of years, and at last the 
patient, if he has not died, recovers from the primary 
disease, and not only recovers but possesses against 
the particular malady in question a special immunity 
which he did not have before. Another phenomenon 
of a most puzzling and incomprehensible kind! 

Finally, the diseases of this class are characterized 
by a third mysterious quality—that which has given 
them their name of the communicable diseases. When 
such a disorder appears in a community which has 
hitherto been free from it—as the influenza came to 
America in October, 1918—it spreads from one per- 
son to another, as fire passes from tree to tree in a 
forest conflagration. Is it any wonder that the ways 
of “the pestilence that walketh in darkness” should 
have awakened the awe and the wonder of mankind? 


PARASITES AND PARASITISM 3 


PRIMITIVE THEORIES OF DISEASE 


The first attempts to explain the origin of the 
plagues and pestilences were naturally based upon a 
belief in supernatural causes. Primitive man walked 
in a world of shadows surrounded by vague and 
unseen spirits of good and evil endowed with passions 
like his own. An epidemic was the visitation of 
some evil demon analogous to the onslaught of a war- 
like human foe, to be met by propitiating the hostile 
spirit or by enlisting the protection of some tribal 
god to combat its malign intent. Preventive medicine 
logically consisted in the use of charms and incanta- 
tions, of amulets and sacred symbols, such as survive 
to the present day in the horse-chestnut carried in 
the pocket to ward off rheumatism, or the bags of 
camphor worn round the neck during the influenza 
outbreak in 1918. 

As is the case throughout the whole realm of 
science, it is to the Greeks that we owe our first 
rational theories of the nature and origin of disease. 
The science which burst into a sudden blaze of glory 
on the rocky islands and capes of the AXgean Sea 
was often crude and faulty; but it was science. It 
involved the assumption of natural physical causes 
for natural physical phenomena. Even when the 
assumptions were erroneous they could be tested and 
proved, elaborated or replaced by better ones. They 
gave us a definite basis for advance, while the re- 
course to a theory of irresponsible supernatural forces 
left no door open for the progressive working of the 
human intellect. 

In the case of the plagues and pestilences the Greek 
theory was particularly faulty. As enunciated by 
the great Hippocrates it attributed these disorders to 
the influence of miasms, subtle emanations in the 
atmosphere, scarcely less mysterious (and scarcely 
more actual) than the demons of an earlier age. It 


4 MAN AND THE MICROBE 


was believed that the plague of Athens was checked 
by lighting fires in the streets to purify the atmos- 
phere from its deadly miasms. 

Yet it was in reality a great step forward to con- 
ceive of an epidemic as due to miasms rather than 
spirits. It opened the way for speculation; and even 
among the Greeks there were those who perceived 
the real nature of these diseases more clearly than 
the official medical leaders of the time. The con- 
tagious nature of the plague was quite definitely 
described by Thucydides, and throughout the later 
periods of classic medicine this conception of con- 
tagion persisted in parallel with the Hippocratic doc- 
trine of miasms. With the spread of leprosy in the 
Middle Ages, beginning about 550 A. D., the prac- 
tise of isolation and quarantine laid down in the book 
of Leviticus became widely current as a method of 
control, culminating in the famous leprosy decretals 
of the third Lateran Council. So effective were the 
measures taken by the princes and bishops of medi- 
eval Europe for the isolation of lepers that this dis- 
ease was practically stamped out by the end of the 
sixteenth century, giving us the first example on a 
large scale of the power of man in controlling the 
plagues and pestilences to which he had hitherto been 
a helpless victim. 

The campaign against leprosy had been favored 
by the fortunate circumstance that this particular 
disease is only slightly contagious. In dealing with 
plague and typhus fever, the science of medieval 
medicine proved ineffective, as was necessarily the 
case when a real knowledge of the nature of under- 
lying factors was almost wholly lacking. Even the 
theory of contagion was applied only to a few of 
those disorders which are really due to its operation. 
Typhoid fever and cholera were still attributed to 
the working of atmospheric miasms and held not to 


PARASITES AND PARASITISM 5 


be contagious. As late as 1865 the leading medical 
authorities of Great Britain taught that the bodily 
discharges of a cholera patient were not dangerous 
until they had become decomposed and generated the 
miasms of disease. Isolation was an instinctive pre- 
caution which even when blindly used was helpful in 
certain instances. So far as a really adequate theory 
was concerned, such as could make possible the gen- 
eral control of communicable disease, the physician 
of 1860 was almost as ill-equipped as his predecessor 
in the time of Hippocrates. 


PASTEUR 


Meanwhile, however, in the dingy laboratories of 
the Ecole Normale at Paris an obscure young French- 
man was eagerly at work on a series of investigations 
which were to open a new world of thought and to 
lift from mankind a large share of the age-long 
burden of preventable disease. 

Louis Pasteur, the son of a humble village tanner, 
was at this time (about 1860) engaged in the study 
of the complex problems o* fermentation. The curi- 
ous phenomena which occur when sugar solutions 
ferment, or milk sours, or organic substances putrefy, 
were generally attributed to the direct action of the 
air. This vague explanation did not satisfy Pasteur. 
He studied fermenting fluids by chemical analysis 
and by the use of the microscope and became con- 
vinced that the minute rod-shaped or spherical or 
oval living things which swarmed in such fluids were 
not present by accident but were intimately connected 
with the production of the changes which were going 
on. By a brilliant series of rigorously controlled ex- 
periments he succeeded in demonstrating beyond the 
shadow of a doubt that these changes in organic sub- 
stances were indeed caused by microbes, and that for 
each particular kind of fermentation or putrefaction 


6 MAN AND THE MICROBE 


a particular kind of microbe was responsible. His 
first great contribution was to establish the germ 
theory of fermentation. 

In 1865 the silk industry, which furnished the 
major means of support for certain departments in 
the south of France, was threatened with extinction 
by the spread of a disease among the caterpillars 
which produce the golden fibers. Pasteur was called 
upon for help. He found in the bodies of the sick 
worms minute corpuscles which looked like the 
microbes he had identified in fermenting wine and 
beer; and by 1870 he had definitely proved that the 
disease of the silkworms was due to these microbes 
and that it could be controlled by breeding worms 
only from stock free from microbes and then pro- 
tecting them from subsequent infection. 

The silkworm industry was saved, but much more 
than this had been accomplished. A first step had 
been taken in the demonstration of the germ theory 
of disease. By 1877 the same proof was furnished 
in regard to a disease called anthrax or splenic fever 
affecting cattle and men, Pasteur himself and Robert 
Koch in Germany completing the demonstration inde- 
pendently and by somewhat different means. In 1882 
came the discovery of the germ of tuberculosis, in 
1883 that of cholera, while in 1884 the microbes 
causing typhoid fever and diphtheria were unmasked. 
From that time to this, the triumphs of bacteriology 
have gone steadily forward to the recent brilliant 
studies conducted at the Rockefeller Institute in New 
York on yellow fever and influenza. Methods of 
research have been broadened and altered in detail, 
but their general lines were laid down by the founder 
of bacteriology sixty years ago. Above all, the spirit 
of Pasteur, the caution, the modesty, the patience, 
the rigorous insistence on the truth, the whole truth 
and nothing but the truth, which characterized his 


| 


| 


: 


PARASITES AND PARASITISM 7 


work, have proved an inestimable inspiration to all 
later investigators in this field. 

With the key furnished by Pasteur it was relatively 
easy to unlock many of the mysteries which had 
shrouded the communicable diseases; and through 
the applications by Joseph Lister of the germ theory 
to antiseptic surgery the operating room and the 
maternity ward of the hospital were robbed of their 
earlier terrors. It is probably safe to say that no one 
man who ever lived has accomplished more than 
Louis Pasteur for the practical well-being of the 
human race and of the races of animals which man- 
kind has domesticated for its uses and its pleasures. 


Tue Usrouitous MIcRroBe 


We realize to-day that the invisible microbes which 
are all about us, in air and earth and water, as well 
as on the surfaces of our bodies, play an important 
part, sometimes for good and sometimes for ill, in the 
affairs of our daily lives. It will be well, therefore, 
to give a brief consideration to some of their char- 
acteristics. 

There are various different kinds of microbes as 
there are different kinds of living things of larger 
size. Some of the microbes are animals, like the 
hookworm which causes so much disease and suffer- 
ing in our own southern States and in most tropical 
countries. Some are smaller and simpler in structure 
but still clearly allied to the animal kingdom, like the 
germ of malaria. Some are so minute that we have 
no real knowledge of their nature. We call them 
“filterable viruses” because they are so tiny that they 
will pass through the pores of a fine porcelain filter 
which holds back most of the microscopic living 
things with which we are more familiar. The most 
abundant, and on the whole, the most important 
microbes, however, belong to a group called the bac- 


8 MAN AND THE MICROBE 


teria whose characteristics we may profitably discuss 
in more detail. 

The bacteria are minute plants related to such low 
forms of life as the molds and yeasts, microbes with 
whose operation every housewife is familiar. They 
have almost no structure, no leaves and stems and 
roots like the higher plants, but are simple single 
cells analogous to the elementary structures out of 
which, as the microscope tells us, the leaves and 
stems and roots of the higher plants are built up. 
Each of these bacterial cells has a wall on the outside 
and a mass of living stuff or protoplasm within. They 
are shaped like sticks (the word bacterium in Latin 
means a stick or rod), or balls or spiral threads, and 
are so small that 400,000,000 could be packed into a 
grain of granulated sugar. Some of them have wavy 
processes or flagella which they use like fins to swim 
about in liquids. Some of them can pass into a 
specially resistant resting stage called a spore, with 
a heavy wall, in which condition they are very re- 
sistant to heat or the action of disinfectants. This 
is almost all that can be seen in regard to their visible 
structure even with the most powerful microscope. 

If the bacteria are small and simple in structure 
they nevertheless possess powers of growth and mul- 
tiplication which are astounding. They normally 
reproduce by the simple process of growing larger 
and then splitting in half, so that two bacteria are 
present where there was only one before; and under 
the most favorable conditions this reproduction may 
take place as often as once in twenty minutes. The 
application of simple arithmetic will show that a 
single germ may at this rate produce a billion de- 
scendants in ten hours. 

Moreover, the bacteria in the course of their repro- 
duction produce profound and far-reaching changes 
in the medium in which they are growing. They 


PARASITES AND PARASITISM 9 


absorb food through their cell walls from the adja- 
cent liquid and in order to secure this food they break 
down the materials in the liquid by discharging 
chemical substances called enzymes which possess 
the power of decomposing the sugar or the protein 
or some other organic compound which will yield up 
what they need. It is in this way that fermentation, 
souring, decay, and all sorts of decompositions of 
organic substances are normally brought about. 
There are a few bacteria floating in the air of 
every room. There are some in every glass of water 
which we drink and on nearly every mouthful of 
food which we consume. There are many thousands 
in every tiny speck of dust or dirt. There are mil- 
lions of them in the mouth, in the intestines, and on 
the skin of every part of the body. Fortunately the 
vast majority are quite harmless and many of them 
are even of direct service and benefit to man. The 
effect upon our lives of microbic growth depends on 
the kind of substance in which the particular type of 
microbe grows and on the kind of chemical change 
which it produces in that substance. The disease bac- 
teria constitute a very small minority able to grow 
in the tissues of the human body, a power which most 
of the group as a whole do not possess. Of the 
majority, adapted for development only in lifeless 
organic substances, those which spoil milk or meat 
which we want to keep sweet are harmful to us. But 
those which produce the particular change which 
transforms milk into buttermilk are beneficial, if 
buttermilk is what we want. In the flavoring of 
butter, in the manufacture of vinegar, in the retting 
of flax, in tanning, and in various other industrial 
processes, bacteria are used with great advantage. 
Above all in the elimination of the dead bodies of 
plants and animals in the woods and fields and in 
various chemical changes connected with the mainte- 


10 MAN AND THE MICROBE 


nance of the fertility of the soil, the bacteria play a 
part of inestimable importance in the cycle of forces 
which make possible life upon our earth. 


THE PHENOMENA OF PARASITISM 


The really dangerous kinds of microbes are those 
which in the course of evolution have acquired the 
habit of living in the human body and at its expense. 
We call the animals and plants which live in this 
way parasites, from a Greek word applied to the 
hanger-on at a great man’s house, and it is perhaps 
wholesome to remember that the habit of parasitical 
living is not limited to the microbic world. In many 
of the major groups of animals between man and the 
microbe there are species which have adopted the 
habit of parasitism, particularly among the insects 
and the worms. Turning to the plant kingdom the 
molds and fungi are by no means the only represen- 
tatives of this habit. The mistletoe owes its sacred 
character to the fact that it keeps green in winter, 
but its brilliant foliage is supported by vital energy 
drawn from the tissues of the oak upon which it lives 
as a parasite. 

There is one interesting thing to notice about the 
parasite in all his manifestations. He has gained 
the power of living in an unusual and abnormal 
environment,—the body of his host, as biologists, 
with a certain unconscious humor, call the victim of 
a parasite; but he has lost something in exchange. 
The human parasite in the Greek drama, if he had 
been living for a long time in this unnatural way, 
had probably forgotten how to earn his living in the 
ordinary hurly-burly of every-day life. Just so the 
parasitic microbe has lost in large measure the power 
to live and grow in water or earth or decomposing 
matter or in any of the other environments in which 
his harmless relatives can thrive. 


PARASITES AND PARASITISM 11 


This is a point of the first importance in connec- 
tion with the spread and the control of communicable 
disease. A parasitic microbe capable of growing in 
the human body can thrive only in the human body 
(or in certain instances in the body of some other 
animal). It may and often does survive for a time 
in water or soil or filth, but only for a time. Disease 
bacteria when outside the human body are almost 
always dying out, and as a rule are dying out with 
great rapidity. There are exceptions to this, as to 
all rules. In milk, for example, certain disease germs 
find a culture medium in which they may grow and 
increase. In water, in earth, in dust and air, how- 
ever, the parasitic microbes quickly perish. 

Let us take water as an example: Sir Alexander 
Houston, the bacteriologist of the London Water 
Board, put some typhoid germs into a bottle of water. 
There were 470,000 of them in one cubic centimeter 
(a small thimbleful) of water at the beginning of 
the experiment. Then he merely let the bottle of 
water stand in his laboratory. At the end of one 
week there were 480 bacteria per cubic centimeter ; 
at the end of two weeks, there were 31; at the end 
of three weeks 5; and at the end of four weeks all 
were dead. 

The discovery that disease germs perish so rapidly 
when removed from the rich warm fluids of the body 
has made it clear that we need not really be afraid 
of many things which our fathers feared in the early 
days of the germ theory of diseases. Fomites (cloth- 
ing, books, toys, or other objects which have been 
used by a sick person) will be dangerous if they 
have recently been handled, but the danger will not 
persist for very long. We can draw no sharp line 
or say that at 4.20 p. m. some object is dangerous 
and at 4.30 p. m., safe. If a person with a cold 
coughs in his hand and then with that hand passes 


12 MAN AND THE MICROBE 


me an apple, I shall be likely to contract that cold. 
If he puts the apple down and leaves the room and 
I come in and pick it up five minutes afterward, the 
danger is much the same. If the apple stays over 
night before I touch it, the risk is less. If it stands 
for a week, there is very little chance that I shall 
become infected. As to the tales of toys put away 
for years and then transmitting disease, we take no 
stock in them at all. 

For the same reasons it seems probable that dust 
in the past has been over-rated as an agent in the 
transmission of disease. Some germs may survive 
drying and it is quite possible to find germs of tuber- 
culosis in the dust of a room which has been occupied 
by a careless patient. The number of such germs 
is very small, however, as compared with the vast 
multitude originally present in the sputum; and the 
reason why the proper care of sputum is so impor- 
tant is much less because of the danger that it may 
dry up and blow about in the form of dust than be- 
cause it may be transferred, while the germs are fresh 
and virulent, by shoes, skirts, fingers, flies, or in some 
other ways. 

The original source of disease germs, then, is the 
human body (or the body of one of the higher 
animals); and the transmission of disease is ordi- 
narily accomplished only by the rather prompt trans- 
fer of bodily discharges from one human being to 
another. 


THE CARRIER 


Bacteriological science has thus relieved us of much 
of the fear which was once entertained in regard 
to dust, fomites, decaying filth, or in general the 
environmental factors once held to be primary factors 
in the causation of disease. On the other hand it 
has revealed new and unsuspected possibilities of 


PARASITES AND PARASITISM 13 


danger among our families and friends and asso- 
ciates by the discovery of the part played by the 
human carrier. 

A “carrier” is a person who is himself well, but 
is cultivating in nose or throat or intestines or gall 
bladder the germs of some disease, against which he 
is immune but which may be transmitted by his bodily 
discharges to any one who lacks the special resistance 
which he himself has acquired. The convalescent 
from typhoid fever for example in a certain propor- 
tion of cases (3 to 4 per cent.) continues to excrete 
typhoid bacilli after recovery is complete; and it has 
been estimated in the past that three or four persons 
out of every thousand in the general population 
might be typhoid carriers (altho the number is prob- 
ably smaller to-day). Diphtheria bacilli are even 
more prevalent in the throats of normal persons, two 
or three out of every hundred showing organisms 
of this type, often not virulent but sometimes actively 
so. Cerebrospinal meningitis and epidemic polio- 
.myelitis are spread largely and perhaps chiefly by 
carriers, and the carrier plays a predominant part 
in the transmission of pneumonia. 

The most famous (or infamous) carrier in the 
history of public health is the cook known as 
“Typhoid Mary,” who between 1902 and 1907 while 
employed in six different families was the cause of 
typhoid cases in every family, infecting 26 persons 
in all. In 1907 she was taken to a hospital and 
found to be a chronic typhoid carrier. She was 
released and was lost to sight for a time; but in 
I915 25 cases of typhoid occurred in the Sloan Hos- 
pital of New York and Mary was found to have 
been employed there. Many other cases were prob- 
ably, tho not certainly, traced to her activities, and 
it is even possible that she was the cause of the 
water-borne outbreak of 1,300 cases at Ithaca, N. Y., 


14 MAN AND THE MICROBE 


in 1903. Another carrier whose story is even more 
surprizing was a farmer who had typhoid fever in 
Wisconsin in 1864. He recovered and moved to 
Camden, N. Y., where he set up in the milk business. 
In 1878 his daughter had typhoid, in 1886 his son- 
in-law, in 1893 another daughter, in 1897 another, 
in 1903 and 1909 two hired men. Meanwhile Cam- 
den became notorious for its generally high typhoid 
rate, three-quarters of the cases being among the 
users of this farmer’s milk. Finally, in 1900, some 
of this milk was sent to New York and caused an 
epidemic of 380 cases, when the New York authori- 
ties investigated, found the man to be a typhoid car- 
rier and cleared up the whole story. 

Jt is the carrier on the one hand and the case of 
disease in the early and unrecognized stage on the 
other which are responsible for the numerous infec- 
tions which arise without previous contact with an 
obvious case. Such infections were wholly mysteri- 
ous before the discovery of the carrier; and it was 
such puzzling cases which were explained by far- 
fetched assumptions as to miasms or fomites. It is 
contact with an incipient case or a carrier which 
usually spreads diphtheria and scarlet fever—not the 
air from a broken drain, or the book which was 
handled by a sick person several weeks ago. 


THE ContTROL OF COMMUNICABLE DISEASE 


It is clear, then, that the original source of disease 
germs is the human case or carrier; that these germs 
generally leave the body in its discharges; that they 
die out rather rapidly when’ removed from their 
normal habitat which is the body itself; and that the 
transmission of disease must therefore be effected 
by the rather prompt transfer of body discharges 
from one human being to another. In formulating 
a program for the control of the communicable dis- 


PARASITES AND PARASITISM 15 


eases it is first of all essential to consider in what 
ways such transfer of infected discharges is most 
likely to be accomplished. It will then be possible 
to devise the best means for breaking the chain of 
infection. 

The agencies by which body discharges may be 
passed from one person to another are commonly 
called the ‘‘vehicles” of disease. The atmosphere, to 
which Hippocrates looked for the origin of epi- 
demics, can not be a vehicle of disease, except in 
so far as coughing or sneezing may produce a fine 
spray in the immediate neighborhood of an infected 
person or by the transfer of disease germs through 
the atmosphere by flying insects. The microbes them- 
selves have no wings and even the mouth spray 
thrown out in coughing is made up of solid particles 
which fall to the ground rather rapidly. Dust is not 
an important or a common vehicle of disease, since 
in the process of drying the vast majority of disease- 
producing microbes will have perished; and for the 
same reason fomites are not particularly dangerous 
unless they have been recently soiled with the dis- 
charge from a sick person or a carrier. In many 
modern hospitals contagious diseases of various kinds 
are cared for in the same ward with only screens 
between the beds to prevent direct infection by moucn 
spray, and so long as care is taken to prevent the 
spread of disease germs by the fingers of attendants 
this system can be used without fear of cross-infec- 
tion. 

The first and most important way in which the 
spread of infection does take place is by contact— 
the more or less direct transfer of discharges by 
mouth spray, by the hands, and by objects which 
have been recently handled. A second class of 
vehicles of infection includes certain articles of food 
and drink—water, and milk, for example—which are 


16 MAN AND THE MICROBE 


exposed to. pollution and are then consumed within 
a short space of time without cooking. A third 
mode in which disease germs are spread is by means 
of certain insects, as the fly and the mosquito, which 
carry the microbes on, or in, their bodies from one 
person to another. These three modes of infection, 
by contact, by food and drink, and by insects, account 
for the vast majority of cases of communicable 
disease. They have been described in alliterative 
form as the “three F’s of sanitation, fingers, food, 
and flies,” “fingers” standing for all forms of more 
or less direct contact, “food” for food and drink of 
various sorts, and “flies” for the many insect vehicles 
of disease. The methods by which each of these 
three main modes of transmitting disease may be 
controlled will be discussed in deta‘l in succeeding 
chapters. 


a 


CHAPTER II 
MUNICIPAL SANITATION 


THe Care oF Bopy DISCHARGES 


HE communicable diseases belong to two main 

groups, those in which the germs are present in 
the discharges from the nose and throat, such as the 
common cold, pneumonia, diphtheria, measles, and 
the like, and those in which the germs are spread 
by the discharges from the intestines and the kid- 
neys, of which typhoid fever and dysentery and 
cholera are examples. The nose-and-throat diseases 
are for the most part spread by contact, and the 
control of these contact-borne infections will be con- 
sidered more fully later on. , 

The germs of the intestinal diseases, on the other 
hand, leave the body in the discharges from the 
bowels and bladder, and these discharges are fre- 
quently transmitted by water or milk or other vehicles 
over a large area and to great numbers of people. 
In the southern part of the United States, and in 
tropical and semitropical countries throughout the 
world, this problem is of peculiar importance, since 
in warm climates typhoid fever, dysentery, and vari- 
ous diseases due to parasitic worms, particularly 
hookworm disease, are all commonly disseminated 
through the improper disposal of human excreta. 
Few of us who live in the sewered cities of the North 
fully realize the importance of this problem; but the 
International Health Board of the Rockefeller Foun- 
dation estimates that out of a total of some seven- 
teen hundred million people inhabiting the globe, 

17 


18 MAN AND THE MICROBE 


over nine hundred million live in countries where 
hookworm infection is a serious menace to health 
and working efficiency. 

Hookworm disease is an example of a communi- 
cable disease in which the process of infection is 
so clearly understood that it gives us an excellent 
picture of what goes on in the case of other maladies 
whose history has been less completely studied. The 
parasites in this case are tiny worms about one-third 
of an inch in length which attach themselves to the 
walls of the intestines and suck the blood of their 
victim, sapping his cnergy and lowering his vitality 
in proportion to their numbers. They reproduce 
and lay eggs which pass out with the intestinal dis- 
charges. The young worms which hatch from these 
eggs are spread about in the soil by casual disposal 
of excreta and penetrate. into the bodies of new 
human hosts in a very curious fashion. In the 
warmer countries the majority of the agricultural 
population go barefoot and these worms bore their 
way through the skin of the foot and after thus 
entering the body find their way to the intestines 
where they attach themselves and continue their 
normal parasitic existence. 

There are two general methods which may be used 
in the control of hookworm disease. By the use of 
certain specific drugs it is possible to destroy the 
worms in the intestine and thus cure the individual 
patient. The fundamental prevention of this disease 
obviously depends, however, on the provision of 
proper facilities for the care of human excreta so 
as to avoid the pollution of soil and the consequent 
infection of new victims. This may be accomplished 
by the construction of tight outdoor closets, screened 
to exclude flies, and with provision for the care of 
the excreta themselves either in pits or in tight re- 
movable receptacles; or best of all, where possible, 


MUNICIPAL SANITATION 19 


by the introduction of a system of water closets and 
sewers. 

In demonstrations carried out in 43 different States 
and countries the International Health Board has 
shown that hookworm disease may be controlled with 
striking success by the application of such methods. 
Thus in Richmond County, Virginia, where this 
work was first begun, the proportion of school chil- 
dren infected with hookworms, which reached the 
enormous figures of 83 per cent. in I9I0, was re- 
duced to 35 per cent. in 1911 and to slightly over 
2 per cent. in 1921. A parallel reduction in other 
intestinal diseases has followed these improvements 
in sanitation. Thus in Troup County, Georgia, be- 
tween 1917 and 1921 the cases of dysentery were 
reduced from 486 to 29 and the cases of typhoid 
fever from 177 to I5. 


Tue DisposaL OF SEWAGE 


The provision of a system of sewers solves the 
problem of waste disposal for the individual house- 
hold in the most satisfactory manner possible. It 
leads, however, to the creation of a new problem 
of municipal sanitation—that of the treatment of the 
sewage itseli—for somewhere at the end of the 
sewerage system the accumulated wastes from all 
the dwellings must somehow be disposed of. 

The sewage of an average American city will 
amount to over 100 gallons a day for every person 
in the population. What this means may best be illus- 
trated by saying that if the daily sewage discharge 
from New York City were collected in the bed of 
a river 100 feet wide and Io feet deep it would com- 
pletely fill it for a distance of 13 miles in one day! 
It is true that this river of sewage is mostly water; 
but the solid matter which it carries with it, tho less 


20 MAN AND THE MICROBE 


than one one-thousandth of the total, would, in the 
case of New York City, be equal to 600 tons a day. 

The damage done by city sewage which is not 
properly disposed of is of two distinct kinds. In 
the first place the disease bacteria which the sewage 
from any large community is sure to carry, may 
pollute water supplies or may cause disease among 
those who bathe in the polluted waters or consume 
shellfish taken from them. In the second place the 
decotnposition of the organic material in the sewage 
may produce offensive conditions along the course 
of the river or harbor into which it is discharged. 

The first of these problems which concerns the 
danger to health is often solved in some other way 
than by the purification of the sewage. It may often 
be more economical and more effective to purify the 
water which is taken out of a stream for drinking 
rather than to attempt to secure a complete purifica- 
tion of all the sewage which may enter it. Shell- 
fish from a polluted area can be made safe by appro- 
priate treatment, and it may prove a better policy 
to abandon a given bathing beach rather than to 
spend money on an elaborate system of sewage treat- 
ment. In one way or another, however, such menaces 
to health must always be controlled. 

In any case the sewage of a city should be so dis- 
posed of that no nuisance shall be created. Some- 
times no special treatment ‘may be necessary. Where 
a small volume of sewage is discharged into a large 
stream or into the ocean, the intestinal bacteria may 
die out and the organic matter be disposed of by 
natural processes without danger of offense. As the 
amount of sewage becomes greater in relation to the 
volume of diluting water it becomes necessary to 
reduce the burden of polluting material. We can 
remove the larger suspended solids in the sewage by 
passing it through screens, or effect a more com- 


MUNICIPAL SANITATION 21 


plete reduction in suspended matter by the use of 
large tanks in which the finer solids settle out. The 
“septic tank” and the “Imhoff tank” are settling 
basins of this kind in which the solids which accumu- 
late on the bottom are digested and reduced in amount 
by the action of putrefactive bacteria. Finally, if 
a higher degree of purification is necessary, the 
organic material in the sewage may be oxidized and 
turned into a harmless and inoffensive mineral form 
(nitrates) by the action of nitrifying bacteria. This 
sort of purification takes place in nature whenever 
manure is ploughed into the soil or when the untidy 
housewife throws kitchen slops out from the back 
door. Ona large scale we can make it more effective 
by disposing of sewage on special beds of sand or 
broken stone or in aeration tanks. All these devices 
involve the cultivation in the sand beds, or on the 
stone filters, or in the aeration tanks, of special types 
of bacteria which, in the presence of sufficient 
oxygen, oxidize the organic matter of the sewage 
into nitrates. In the case of the sand filter the 
sewage is applied in intermittent doses, the air being 
drawn in after each application. In the stone filters, 
called trickling beds, the sewage is discharged from 
spray nozzles up into the air, and then allowed to 
trickle downward over the stones which are covered 
with bacterial films. In the aeration tanks air is 
blown directly in through porous plates at the bottom 
and sewage, oxygen, and nitrifying bacteria are thus 
intimately mixed. 

By a proper combination of these various devices 
it is possible to secure any result which we desire 
in the purification of sewage. There is one case of 
a village on the shores of the water supply of a 
large city whose sewage is first settled, then passed 
through two successive stone beds, settled again, 
passed through a sand filter and then disinfected 


22 MAN AND THE MICROBE 


with chlorin, producing an effluent purer and better 
than the water supply into which it is discharged. 
Such elaborate treatment is, of course, very rarely 
needed; and in a given case the aim should be to 
protect the public health and secure freedom from 
nuisance at the minimum possible cost in view of 
all local conditions, remembering the old maxim 
that “an engineer is a man who can do for one dollar 
what any fool can do for two.” 


THE PROBLEM OF WATER-BORNE DISEASE 


It is natural to pass from a consideration of the 
problem of sewage disposal to that of water supply, 
since in the past the mingling of sewage with drink- 
ing water has so often been attended with disastrous 
results. 

Our water supply comes originally from the rain- 
drop; and the water which condenses into a rain-drop 
has previously been distilled in the form of purest 
vapor from the surface of lake, stream, or ocean, 
or from the leaves of trees or other evaporating sur- 
faces. As the drop forms and as it passes downward 
through the air it takes up a certain amount of 
foreign matter in the form of dust or gases, but 
such foreign materials are small in amount and of 
no sanitary significance. For practical purposes the 
rain water is pure when it reaches the surface of the 
earth. Here, however, its contamination promptly 
begins. As the rain washes the roofs of buildings, 
the streets of cities, the soil of barnyards and agri- 
cultural land it takes up large quantities of material 
in solution and suspension, including vast numbers 
of bacteria of all sorts; and if human excreta are 
anywhere exposed these bacteria will include numer- 
ous representatives of the intestinal flora and often 
some of the microbes capabie of producing typhoid 
fever or other intestinal disease. 


MUNICIPAL SANITATION 23 


The surface wash thus produced by a rain-storm 
then divides itself into two portions. A part flows 
off by way of the brooks and rivers and lakes, con- 
tinuing. to form a portion of the surface waters 
of the globe. The rest trickles downward through 
the soil and joins the great reservoirs of what we 
call the ground waters, slowly passing through the 
soil toward river, lake, or ocean with which they 
ultimately mingle by subterranean routes. 

As the surface waters pass into larger and more 
sluggish streams and lakes they gradually become 
purified from their original pollution by sedimenta- 
tion, oxidation, and the dying out of the intestinal 
bacteria, and the ground waters are purified in even 
greater degree by the filtering action of the soil. In 
too many instances, however, new pollution enters 
by sewers discharged into the surface waters or 
reaching the ground waters through cracks and fis- 
sures in the soil; and the use of such waters, or of 
those exposed to recent washings from the surface 
of polluted soil, is fraught with the gravest dangers 
to life and health. 

The first striking example of water-borne disease 
which occurred in the United States was at Plymouth, 
Pennsylvania, in 1885. The water supply of the city 
was derived from four small reservoirs, near one of 
which were a few scattered houses. A man living in 
one of these houses visited Philadelphia and con- 
tracted typhoid fever there, returning home in Jan- 
uary. His excreta were thrown out on the frozen 
ground sloping down toward the water supply, and 
when the thaw came in March the polluting material 
was washed in, sufficient to cause 1,104 cases of 
typhoid fever in Plymouth out of a total’ population 
of 8,000. In 1890-91, excreta discharged into a 
branch of the Merrimac River caused 550 cases of 


24 MAN AND THE MICROBE 


typhoid fever in Lowell, Massachusetts, which used 
the river water for drinking, and the sewage of 
Lowell was then carried on to Lawrence, nine miles 
below, producing over 200 cases there. Excreta from 
a single case of typhoid fever washed into a reservoir 
caused 514 cases of typhoid in New Haven, Con- 
necticut, in 1901; and the story of such instances 
could be repeated almost without limit. 

It is such instances as these which have at last 
taught the folly of using for drinking the water 
from any source not definitely proved to be free 
from pollution. In the case of surface water, ex- 
perience has shown that no surface supply is abso- 
lutely safe unless effective safeguards have been 
supplied in the way of some purification process; and 
in the case of ground waters where we can not detect 
the presence of possible pollution by direct inspection 
we must rely on bacteriological analyses to determine 
whether there is liability of danger. 


THE PURIFICATION OF WATER SUPPLIES 


Fortunately we now have at our disposal simple 
and efficient and economical means of treating pol- 
luted water so as to make it safe for drinking; and, 
as a result of the application of such treatment, water- 
borne disease has in civilized countries become almost 
a thing of the past. 

The first method of purification which can be util- 
ized is storage. We have already pointed out that 
if water is held for a considerable period the intesti- 
nal bacteria present die out with considerable rapidity, 
so that after a lapse of several weeks even a highly 
polluted water will be rendered harmless. In sup- 
plies drawn from lakes this purifying agency always 
enters to a more or less considerable extent; and 
when any large city derives its water supply from a 


MUNICIPAL SANITATION 25 


flowing stream, an artificial storage reservoir is 
generally introduced to equalize the available flow. 
The efficiency of purification by storage can not, 
however, be estimated by the capacity of a reservoir 
alone. Experience has taught us that local currents 
due to wind action or some other condition may carry 
fresh pollution for a long distance in a short period 
of time. This method of purification must therefore 
be watched with the greatest care and controlled by 
constant bacteriological examinations before we can 
place reliance upon its efficiency. 

A second and more trustworthy method of treat- 
ing polluted water is known as slow sand filtration 
and consists in passing the water slowly through a 
bed of suitable sand from four to six feet deep. 
Such a sand bed acts as a filter, the bacteria present 
in the water clinging to the sand grains and to the © 
fine material and the bacterial growth which gathers 
at the surface of the bed, so that the effluent which 
flows off at the bottom will be as safe as a good 
spring water. Even such polluted waters as those 
of the Merrimac and the Hudson Rivers may in this 
way be made quite safe for use. 

The slow sand filter works admirably with the 
clear river waters of New England. In the Middle 
West, however, the rivers often come from regions 
where the soil is largely clay and such waters carry 
a fine turbidity which interferes very seriously with 
the process. For such waters we have a third method 
of purification which is called rapid mechanical fil- 
tration. In this mode of treatment we again use a 
sand filter but we reinforce the filtering action of the 
sand by adding a chemical, such as sulfate of 
alumina, which forms a heavy precipitate on the 
surface of the sand, and then pass the water through 
at a much more rapid rate. For turbid waters this 


26 MAN AND THE MICROBE 


is the most efficient and economical method at our 
disposal. 

Finally, water may be purified by chemical disin- 
fection, the process generally used consisting in the 
addition either of bleaching powder or of chlorin 
gas. Chlorin is a powerful oxidizing agent and 
destroys the vast majority of the bacteria present in 
a very few moments without producing any appreci- 
able change in the final composition of the water. 
The chief limitation to the use of this process lies in 
the fact that in order to be effective the amount of 
chlorin added must be nicely proportioned to the 
organic matter present in the water. If the organic 
content of the water increases suddenly, as is the 
case with river waters after a rain, the chlorin 
will be used up by the organic matter before it can 
kill the bacteria. The ideal field for chlorin treat- 
ment is to put the finishing touches on a water which 
has already been fairly well purified by storage or 
filtration. In combination with one or the other of 
these processes it is used by a large majority of cities 
in the United States. 

The advantages of a safe water supply are so 
obvious that it is quite inexcusable for any community 
to take risks with a supply that is not fully pro- 
tected by one of the methods discussed above. At 
Lawrence, Massachusetts, for example, the cost of 
purifying the city water amounted to about sixty 
cents per capita yearly. It was conservatively esti- 
mated that the reduction in typhoid fever effected 
by this filter involved an economic saving equivalent 
to over ten dollars per capita yearly. The introduc- 
tion of filtration and disinfection processes has been 
the chief, but by no means the only, factor in reduc- 
ing the typhoid fever death rate of the United States 
Registration Area from 36 per 100,000 persons in 
1890 to less than 8 per 100,000 in 1920. 


MUNICIPAL SANITATION 27 


Miixk SuppLty AND DISEASE 


Next to water, milk has perhaps been the one arti- 
cle of food most commonly associated with the spread 
of communicable disease. If one considers for a 
moment the conditions surrounding the production of 
milk it will be obvious that there are many possibili- 
ties of danger, in some respects even more than in the 
case of water supply. Milk comes, not from the 
clouds, but from the body of an animal which may 
or may not be diseased. It is collected in stables 
which are rarely as clean as the sandy shores of a 
well-protected reservoir. Instead of being trans- 
ported in a system of closed pipes it is exposed at 
a dozen points on the cityward way to contact with 
human beings who may be carriers or incipient cases 
of disease. Above all, however, we can have no re- 
liance here upon the purifying agency of storage, 
for milk is one of the few media in which disease 
germs may actually increase and multiply during 
transit. 

Milk may produce disease in three different ways. 
In the first place it may transmit specific bacteria 
from the infected cow to man, particularly in the 
case of tuberculosis—and a considerable proportion 
of tuberculosis in young children is beyond question 
caused in this way. In the second place milk may 
become infected by human contact with the germs of 
various diseases, such as septic sore throat, typhoid 
fever, diphtheria, and scarlet fever, hundreds of epi- 
demics having been traced to this source. Finally, 
there is the closest connection between cow’s milk 
of low quality and the summer diarrheas of children, 
and it appears probable that these summer diarrheas 
are caused not necessarily by specific infection but 
by the development in the milk of miscellaneous putre- 
factive and fermentative bacteria. 

The danger of milk-borne tuberculosis cay be 


28 MAN AND THE MICROBE 


avoided by the testing of cattle with tuberculin and 
the elimination from dairy herds of all animals 
which show a reactance to this test. So far as the 
decomposition of milk is concerned much may be 
accomplished by dairy inspection, the use of clean 
utensils, and particularly the careful cooling of milk 
in transit to avoid undue multiplication of bacteria. 
It is possible by a combination of these methods to 
produce a small amount of milk of high quality 
and high cost which will be clean and sweet and free 
from the germs of tuberculosis. Even such a product, 
which we call certified or selected milk, can never, 
however, be quite free from the danger of human 
infection since there is always the possibility that 
an unsuspected carrier may cough over a pail or 
touch the neck of a can; and a single such contact 
may produce deadly results. 

Fortunately we have here, as in the case of water 
supply, a method of purification which will render 
milk really safe as well as clean and which can be 
applied at so low a cost as to be used with success 
in making the whole milk supply of a city fit for 
human consumption from a sanitary standpoint. This 
method is called pasteurization, after Louis Pasteur 
who first used it for the preservation of organic 
fluids, and it consists in the heating of the milk 
to a temperature of 140° to 145° Fahrenheit and 
holding it at that temperature for 20 to 30 minutes. 
This process destroys the vast majority of bacteria 
present in milk, including all disease germs and, if 
properly applied, it in no way alters the taste or 
the digestibility or the food value of the milk, except 
for the partial destruction of one particular vitamin 
(which protects against the disease, scurvy). Even 
raw milk does not supply this special vitamin in re- 
liable quantity, so that infants fed on cow’s milk, 
whether raw or pasteurized, should be given an anti- 


MUNICIPAL SANITATION 29 


scorbutic such as orange or tomato juice. It can 
not be too strongly emphasized that no raw milk 1s 
ever a wholly safe source of supply for children. 
t should be, and is, the effort of all active health 
authorities to secure the effective pasteurization of 
all milk except the small amount of milk of Certi- 
fied or Grade A quality; and even the latter can 
profitably be pasteurized in the home before it is 
used for infant feeding. 


SANITARY PROBLEMS OF Foop Supply 


Water and milk supplies have enjoyed a sinister 
preeminence as factors in the spread of disease upon 
a wholesale scale, on account of their liability to 
pollution and the fact that they have so generally 
been consumed without the salutary disinfecting ac- 
tion involved in most processes of cookery. How- 
ever, epidemics have also been traced to various other 
raw foods, celery, lettuce, water cress, and, particu- 
larly, oysters and other shellfish. With increasing 
care in the supervision of the grounds from which 
oysters are taken and with the practical elimination 
of the practise of “floating” or “fattening” oysters 
by placing them in brackish water (which causes 
them to swell up and look plumper), disease due to 
this cause has become relatively rare. Furthermore, 
it has been shown that even oysters taken from scme- 
what polluted sources may be rendered safe by stor- 
ing them for a short time in chlorinated sea water 
and this process is in actual use at one or two 
places along the Atlantic seaboard. 

Either cooked or uncooked foods may of course be 
infected by the “carrier in the kitchen,” and numerous 
outbreaks of typhoid fever, paratyphoid fever, and 
“food poisoning” have been caused in this way. If 
the infective material be thoroughly mixed with the 
food, the bacteria inside may even survive the ordi- 


30 MAN AND THE MICROBE 


nary processes of cookery, as in the famous epidemic 
of typhoid fever at Hanford, California, where 93 
people who attended a church supper were infected 
by a dish of Spanish spaghetti prepared by a typhoid 
carrier. In certain instances food poisoning may 
be caused by bacteria of the paratyphoid group pres- 
ent in the meat from diseased animals, and very 
recently the bacteriologists of the New York City 
Department of Health traced an epidemic to the con- 
tamination of cream puffs by mouse excreta. It 
will usually be found on close study that such out- 
breaks are due to specific infection with bacteria 
of the typhoid-paratyphoid group from human or ani- 
mal sources; and the term “ptomaine poisoning” 
implying that decay is the principal factor is a mis- 
nomer. Decay in itself is hy no means necessarily 
harmful if specific disease-producing organisms be 
absent, as is shown by the fact that certain cheeses 
are habitually consumed in a state of decomposition, 
and by the preference of epicures for game that is 
a trifle “high.” Protection against such diseases 
must be sought by inspection of animals before and 
after slaughter, by cleanliness in the preparation 
of foods, and by the exclusion, so far as possible, 
of carriers from the business of food-handling. 
There is one other type of food poisoning of a 
different nature which deserves special mention— 
the disease known as botulism, which attracted so 
much attention after the war in connection with 
outbreaks traced to the consumption of ripe olives. 
The germ of this disease is rather widely distributed 
in soil and on fruits and vegetables in certain regions, 
and in foods which have been preserved by faulty 
methods it develops and produces a very powerful 
toxin. Protection against this disease can be easily 
insured by care in the processes of food preservation. 
As in the case of the paratyphoid food poisonings, 


MUNICIPAL SANITATION 31 


there is no necessary and universal relation between 
obvious decomposition and danger to health; but 
foods in which the bacillus of botulism has multiplied 
have generally been distinctly “off-color” in odor 
or taste. It is therefore a good rule to avoid any 
food that displays any such abnormalities. 


CHAPTER III 
INSECTS AND DISEASE 


TuHeE FittHy Fry 


W E may pass next to the second important mode 
of spreading of disease—through the medium 
of insects. The relation of insects to disease may 
be of diverse sorts. In some instances the germ 
of a particular disease is transmitted by a particular 
type of insect and in no other way. In other in- 
stances the relation between the insect and the disease 
may be merely an occasional and accidental one. 

The part played by the fly in the dissemination of 
typhoid fever is of the second type. Typhoid fever 
is spread by water, by milk, by foods, by direct con- 
tact, and in various other ways; but if conditions 
are such that flies may gain access, on the one hand, 
to human excrement and, on the other, to food, they 
may and do play an important part in its dissemina- 
tion. During the Spanish War when one in five 
of our volunteer soldiers suffered from typhoid fever 
the fly was the chief agent at fault. Dysentery and 
diarrhea may also be transmitted in a similar fashion, 
and even in sewered cities like New York flies play 
a definite role in the spread of infant diarrhea. 

One of the most important steps in the prevention 
of fly-borne disease is the proper disposal of human 
excreta, as discussed in a preceding chapter. We 
may cite here the experience of Jacksonville, Florida, 
as an illustration of the importance of such precau- 
tions. A campaign for the rendering fly-proof of 
yutside closets throughout this city reduced the 

32 


INSECTS AND DISEASE 33 


typhoid death rate of the city from 106 to 26 per 
100,000 population. 

The most effective means of dealing with irsect- 
borne disease is always to be found in controlling the 
breeding of the insect itself; and for this purpose 
we must know something of its habits. The ordinary 
house-fly—better called the filthy fly, since it ought 
not to be an accepted guest in our habitations— 
breeds by preference in horse manure but will lay 
1ts eggs in almost any kind of moist-decaying organic 
matter. The larve which hatch from these eggs 
are whitish maggots which crawl about and feed 
in the manure or other material for five days to a 
week and then burrow down into the ground or our 
into the dry edges of the manure heap where they 
go into the pupa stage, a little brownish chrysalis, 
like that which we find inside the cocoon of a moth. 
From this pupa after a few more days the adult 
fly emerges. 

The control of the fly, therefore, depends on 
the elimination of decaying organic matter in which 
it may breed, and particularly on the care of stable 
manure, which should be stored in covered tight- 
bottomed bins from which the larve can not escape 
and removed from the vicinity of human habitation 
at least once a week. Adult flies may be reduced 
in numbers by the use of traps which are made with 
a wire cone having some attractive bait below and 
opening at its smaller end into a cage of wire. The 
flies after seeking the bait pass upward through the 
cone toward the light into the cage and are unable 
to find their way out again. Screening of windows 
and the use of fly paper and fly poisons are useful 
palliatives, but “swatting the fly” is an ineffective 
procedure and the only real solution of the problem 
lies in the systematic and rigorous control of the 


34 MAN AND THE MICROBE 


sanitary conditions which make continued fly-breed- 
ing possible. 


MosgQuiITors AND MALARIA 


The most important of the insect-borne diseases 
from a world-wide viewpoint, and considering sick- 
ness and disability as well as direct mortality, is no 
doubt malaria, which Sir William Osler, the great 
physician, justly called “the greatest single destroyer 
of the human race.” The secret of this mysterious 
malady—the bad air disease (mal’ aria)—was re- 
vealed in 1898 when it was discovered that the 
infecting germ was transmitted by the bite of mos- 
quitoes of the genus Anopheles, and in no other way. 
Its connection with night air, marshy areas, and 
excavated soil was at once explained by the fact 
that these mosquitoes breed in stagnant water, and 
there was placed within our grasp a simple and 
effective method of controlling this disease through 
measures directed against its insect host. 

The eggs of the mosquito are laid upon the surface 
of the water, and the larve which hatch out are 
little brownish or blackish wigglers which jerk them- 
selves about in the water in a characteristic fashion 
and come up to the surface to breathe. After a few 
days the larve change to pups, little seed-like ob- 
jects which still move about actively but do not feed, 
and from these pupz the adult mosquitoes emerge, 
standing on the floating pupa skin at the surface 
of the water until their wings have dried and they can 
fly away. 

If one is troubled with mosquitoes it is a simple 
matter to search out their breeding places by hunting 
for small protected bodies of standing water, clogged 
streams, flooded areas, pools, rain barrels, roof gut- 
ters, and the like, and dipping up water in a white 
lined vessel to see whether it contains wigglers. 


INSECTS AND DISEASE 35 


The Anopheles larvz can be distinguished from the 
larve of the common mosquito, Culex, by the fact 
that when resting at the surface of the water they 
lie parallel with it, while the Culex larve hang 
down at an angle, touching the surface only with their 
long breathing tubes. The adult mosquitoes are also 
easily distinguished by the fact that Anopheles has 
spotted wings and Culex, clear wings, and by their 
resting position on a wall, Culex standing in a slightly 
humped position, its head pointing toward the wall 
and its body parallel with it, while Anopheles stands 
at an angle with the wall, beak, head, and body all 
in a straight line. 

The most effective way of controlling mosquitoes 
is obviously to drain the marshes and remove all the 
small accumulations of stagnant water, for these in- 
sects will not breed in large open ponds or clear 
flowing streams. Where drainage is unduly costly 
the wigglers may be destroyed by spraying oil on 
the marsh lands, since the oil spreads in a thin 
layer over the surface, and makes it impossible for 
the insects to get to the air to breathe, or by stocking 
small ponds with fish which eat the wigglers. Screen- 
ing of houses is of great assistance in the control of 
malaria, and we have still another means of combat- 
ing this disease by the systematic use of quinin to 
cure those who are ill, to eliminate the germs from 
the blood of carriers, and to protect those who are 
well against their entrance. 

The International Health Board has carried on a 
series of striking demonstrations of the value of 
malaria control measures in various southern States 
and tropical countries and has demonstrated that by 
the control of mosquito breeding areas, by scre:#- 
ing, or by the systematic use of quinin, it is possible 
to eliminate from four-fifths to nine-tenths of the 


36 MAN AND THE MICROBE 


malaria in the worst infected districts at a cost which 
generally amounts to between fifty cents and a dollar 
per inhabitant a year. The money loss due to malaria 
in the United States has been estimated at $100,000,- 
ooo a year, and it is obvious that it will prove well 
worth while from a purely economic standpoint to 
take vigorous steps to eradicate this disease and lift 
the burden of disability which it lays upon the 
shoulders of our southern populations. 


THe CoNQUEST OF YELLOW FEVER 


The discovery of the mode by which malaria is 
transmitted opened the way for the most dramatic 
episode in the history of public health—the conquest 
of yellow fever. The disease, since the days of the 
ancient Maya civilization, had been the curse of 
tropical America. From this region of endemic 
prevalence it spread to the United States in every 
year between 1800 and 1879 with but two exceptions. 
In 1793, a tenth of the population of Philadelphia 
perished from its ravages. When the American 
Army of Occupation entered Cuba in 1898, yellow 
fever was one of the major problems with which 
it was confronted, and the origin of the disease was 
still a complete mystery. In the words of a report 
issued by the United States Public Health Service 
in that year “fone has not to contend with an organism 
or germ which may be taken into the body with food 
-or drink, but with an almost inexplicable poison 
so insidious in its approach and entrance that no trace 
is left behind.” 

At this very time, however, the mosquito theory of 
the transmission of malaria had just been established. 
When a commission of army surgeons, including 
Reed, Carrel, Lazear, and Agramonte, was sent to 
Havana in 1900 they naturally turned to a similar ex- 


INSECTS AND DISEASE 37 


planation for the causation of yellow fever. What 
followed has been elsewhere described in the follow- 
ing words :* 

“The lower animals were not known to suffer from 
yellow fever, so that experiments upon human sub- 
jects were essential. In the words of Dr. Kelly’s 
life of Major Reed, ‘after careful consideration, the 
Commission reached the conclusion that the results, 
if positive, would be of sufficient service to humanity 
to justify the procedure, provided, of course, that 
each individual subjected to experiment was fully 
informed of the risks he ran, and gave his free con- 
sent. The members of the Commission, however, 
agreed that it was their duty to run the risk involved 
themselves, before submitting any one else to it.’ 

“The first successful experiment was made with 
Dr. Carrel, who allowed himself to be bitten on 
August 27 by a mosquito which had previously bitten 
four yellow fever patients. Four days later he was 
taken sick and for three days his life hung in the 
balance. Both he and Private W. H. Dean, the 
second case produced experimentally in the same 
way, recovered. Dr. Lazear, however who came 
down with the disease, not as a result of the experi- 
mental inoculations to which he also had submitted, 
but from an accidental bite, was less fortunate than 
his colleagues, for a week later he died, after several 
days of delirium. 

“An experimental station, named ‘Camp Lazear’ 
after this first martyred member of the party, was 
established in the open country; and to the lasting 
honor of the United States Army, volunteer subjects 
for the experiments from among the troops were 
always in excess of the demand. Private John R. 


1 Winslow, C.-E. A. “The Evolution and Significance of the 
Modern Public Health Campaign.” Yale University Press. New 
Haven, 1923. 


38 MAN AND THE MICROBE 


Kissinger and John J. Moran, a civilian employee, 
were the first to volunteer ‘solely in the interest of 
humanity and the cause of science,’ their only stipu- 
lation being that they should receive no pecuniary 
reward. 

“The result of the experiments carried out at Camp 
Lazear proved beyond peradventure that yellow fever 
was transmitted by the bite of a certain mosquito, 
Aédes calopus, and in no other way, for non-immunes 
who lived for twenty days in a small, ill-ventilated 
room, in which was piled clothing and bedding, loath- 
some with the discharges of yellow fever patients, 
all escaped infection, so long as they were protected 
from the bites of mosquitoes. 

“On the memorial tablet to Lazear in the Johns 
Hopkins Hospital is the inscription: ‘With more 
than the courage of the soldier, he risked and lost 
his life to show how a fearful pestilence is communi- 
cated, and how its ravages may be prevented.’ The 
same risk was freely taken by each member of the 
party from major to private. The result of their 
devotion is indicated in two of Reed’s letters to his 
wife: ‘Six months ago, when we landed on this 
island, absolutely nothing was known concerning the 
propagation and spread of yellow fever—it was all 
an unfathomable mystery—but to-day the curtain 
has been drawn’; and later, on New Year’s Eve; 
‘Only ten minutes more of the old century remain. 
Here have I been sitting reading that most wonderful 
book, “La Roche on Yellow Fever,” written in 1853. 
Forty-seven years later it has been permitted to me 
and my assistants to lift the impenetrable veil that 
has surrounded the causation of this most wonderful, 
dreadful pest of humanity and to put it on a rational 
and scientific basis. I thank God that this has been 
accomplished during the latter days of the old cen- 


INSECTS AND DISEASE 38 


tury. May its cure be-brought out in the early days 
of the new.’ 

“The practical result of this Hmcorery was im- 
mediate and striking. In the half-century or so for 
which we have records, yellow fever had killed an 
average of 750 persons a year in the City of Havana. 
The sanitary reforms introduced by the American 
Army of Occupation which produced good results 
in reducing typhoid and smallpox had been powerless 
against yellow fever because its cause was as yet a 
mystery. Following immediately on the experiments 
at Camp Lazear, on February 15, 1901, a campaign 
was begun on the new lines indicated, by screening 
the rooms occupied by yellow fever patients and 
destroying all mosquitoes in the neighborhood. As 
a result there were six deaths in the City of Havana 
during the year 1901 as against 305 in the preceding 
year, and altho sporadic cases have been introduced 
from other localities, yellow fever has never again 
established itself in Havana. The scourge of cen- 
turies was wiped out in a single year. 

“Tt was the demonstration of yellow fever control 
at Havana which, four years later, made possible 
the building of the Panama Canal; and throughout 
the Torrid Zone has opened up the Tropics for the 
occupancy of the white race. During the last few 
years the International Health Board has actively 
embarked upon the aggressive warfare of extermina- 
tion against yellow fever outlined by the late General 
Gorgas. At Guayaquil, once the chief endemic center 
of this disease, it has been eradicated. During 1921, 
Honduras, Nicaragua, Ecuador, and Costa Rica were 
immune from the disease; Guatemala and Salvador 
had no cases later than February; by July, Peru, 
and by November, British Honduras, were free of 
infection. The complete eradication of yellow fever 
from the earth is within the bounds of our vision." 


40 MAN AND THE MICROBE 


PLAGUES OF THE OLDEN TIME 


Scarcely less ,spectacular than this victory over 
yellow fever is Be success which modern sanitary 
science has made possible in dealing with the two 
great pestilences of the Middle Ages, typhus fever 
and bubonic plague. 

Typhus fever, the “ship fever,” “camp fever,’ and 
“Jail fever” of olden times, is the disease which deci- 
mated the troops of Napoleon in the retreat from 
Moscow and which constantly hung like a black 
cloud along the track of armies. With increasing 
habits of personal cleanliness this disease gradually 
disappeared from civilized communities but continued 
to smoulder in southeastern Europe, in Mexico, and 
in other backward areas of the globe. With the out- 
break of the Balkan Wars typhus developed to grave 
epidemic proportions in Serbia, b t in 1909 Nicolle 
discovered that this disease was transmitted by the 
bite of the body louse, cnd it was clear that a simple 
routine of cleansing bodies and clothing could be 
relied upon to check its ravages. ‘Throughout the 
Great War typhus was kept under control—to burst 
out once more in gigantic conflagration with the 
breakdown of civilization in revolutionary Russia. 
In 1921, the whole world was menaced with an in- 
vasion more deadly than that of the Red Armies; 
but in Poland, where the principal battle line was set, 
the Polish Sanitary Administration, aided by the 
Epidemic Commission of the League of Nations, 
established quarantine stations, disinfecting plants, 
and hospitals which were completely successful in 
checking the westward spread of the disease. 

In similar fashion the progress of sanitary science 
has robbed bubonic plague of its terrors. This 
disease, the “Black Death” of the Middle Ages, has 
twice spread over the whole of the known world, 
killing one-fourth of the population of Europe in 


3? 66 


INSECTS AND DISEASE 41 


the fourteenth century, and in 1665 producing in 
London the horrors immortalized by Defoe in his 
Journal of the Plague Year. In 1871, plague again 
broke out in China and Eastern Siberia and passed 
on to India, where it killed six million victims in 
a period of ten years. This time, however, it con- 
fronted a new force, the organized force of modern 
science. In Japan, the germ was discovered, and 
it was shown that the plague was primarily a disease 
of rats, marmots, ground squirrels, and similar ani- 
mals. In India, it was shown that the germ is trans- 
mitted from rat to rat and from rat to man by the 
flea. The modern method of plague control is built 
chiefly upon the eradication of rats, by trapping, 
poisoning, and above all by eliminating rat-breeding 
places, and upon a system of quarantine which in- 
cludes the destruction of rats upon ships coming 
from infected ports. During the past twenty years 
plague has at times spread to ports all over the world 
—in Australia, in England, in Brazil, in Texas, 
Louisiana, and California. In certain parts of Cali- 
fornia the ground squirrels have become infected so 
that a permanent focus of plague exists in this coun- 
try. Yet everywhere, except in India, the disease 
has been held in check by vigorous anti-rat cam- 
paigns wherever a human case occurs or a rodent 
case in the vicinity of human habitations. In no 
well-organized community have we to-day the slight- 
est fear of a real plague epidemic. 

So far as all the insect-borne diseases are con- 
cerned, it may, indeed, be said that they are now 
wholly within our control. The endemic centers of 
plague, typhus, and malaria are more widespread 
than those of yellow fever, and complete eradication 
of these diseases from the surface of the globe may 
not be within the immediate bounds of possibility. 


42 MAN AND THE MICROBE 


In any given community, however, we know exactly 
what to do in order to hold these diseases in check, 
and their control depends simply on the appropriation 


of the necessary funds and their expenditure by 
qualified sanitary authorities. 


CHAPTER IV 
THE CONTACT-BORNE DISEASES 


NATURE AND SIGNIFICANCE OF CONTACT INFECTION 


Wi the progressive control of foods and of 
insects as vehicles of disease, the relative im- 
portance of the third mode of infection—by more or 
less direct contact—has come to occupy more and 
more of the attention of the sanitarian; and unfor- 
tunately the difficulties in the way of control are here 
very much greater than in the case of either of the 
other two groups. 

The paths by which contact infection may spread 
are almost infinite in number. The most direct type 
of transfer is that which occurs when an infected 
person coughs or sneezes in the face of a susceptible 
victim, as may happen whenever people are crowded 
together, in a street car or in some congested place of 
public assembly. From such an extreme case we 
pass through innumerable more roundabout types of 
transfer in which germs pass from the mouth of the 
infected person to the hands of the infected person, 
thence to various objects, such as door knobs, faucets, 
push buttons, money, and the like, and finally to the 
hands of the new victim or to some article of food 
and back to the mouth again. As we have pointed 
out in an earlier chapter there is no sharp line to be 
drawn between contact and fomites infection. The 
only essential for the dissemination of disease is that 
the discharges from one mouth shall be carried to 
another mouth without too considerable a lapse of 
time. 


43 


44 MAN AND THE MICROBE 


As Dr. C. V. Chapin has pointed out:* “Probably 
the chief vehicle for the conveyance of nasal and oral 
secretions from one to another is the fingers. If one 
takes the trouble to watch for a short time his neigh- 
bors, or even himself, unless he has been particularly 
trained in such matters, he will be surprised to note 
the number of times that the fingers go to the mouth 
and the nose. Not only is the saliva made use of for 
a great variety of purposes, and numberless articles 
are for one reason or another placed in the mouth, 
but for no reason whatever, and all unconsciously, the 
fingers are with great frequency raised to the lips or 
the nose. Who can doubt that if the salivary glands 
secreted indigo the fingers would continuaily be 
stained a deep blue, and who can doubt that if the 
nasal and oral secretions contain the germs of dis- 
ease these germs will be almost as constantly found 
upon the fingers? All successful commerce is recip- 
rocal, and in this universal trade in human saliva-the 
fingers not only bring foreign secretions to the mouth 
of their owner, but there, exchanging them for his 
own, distribute the latter to everything that the hand 
touches. This happens not once but scores and 
hundreds of times during the day’s round of the indi- 
vidual. The cook spreads his saliva on the muffins 
and rolls, the waitress infects the glasses and spoons, 
the moistened fingers of the peddler arrange his fruit, 
the thumb of the milkman is in his measure, the 
reader moistens the pages of his book, the conductor 
his transfer tickets, the ‘lady’ the fingers of her 
glove. Every one is busily engaged in this distri- 
bution of saliva, so that the end of each day finds 
this secretion freely distributed on the doors, window 
sills, furniture, and playthings in the home, the straps 
of trolley cars, the rails and counter and desks of 


1 Chapin, C. V. ‘‘The Sources and Modes of Infection.” John 
Wiley and Sons. New York. igro. 


THE CONTACT-BORNE DISEASES 45 


shops and public buildings, and, indeed, upon every- 
thing that the hands of man touch. What avails it if 
the pathogens do die quickly? A fresh supply is 
furnished each day.” 

The intestinal diseases, such as typhoid fever, may 
be, and often are, transmitted by direct contact, since 
polluting material from the intestinal discharges by 
no means infrequently finds its way to the fingers. 
The contact-borne diseases par excellence are, how- 
ever, those in which the specific germs are present 
in the discharges from the nose and throat; and a 
moment’s consideration will indicate that in this class 
are included the great majority of the communicable 
diseases with which we have to deal. Discharges 
from the upper respiratory tract are the primary 
sources of infection, not only in such diseases as the 
common cold, diphtheria, influenza, mumps, pneu- 
monia, septic sore throat, tuberculosis, and whooping 
cough whose symptoms are obvious in throat, nose, 
and lungs, but also in the eruptive diseases, chicken- 
pox, German measles, measles, scarlet fever, and 
smallpox, and in infant paralysis and epidemic cere- 
brospinal meningitis where the seat of the actual dis- 
ease is in the central nervous system. 

The control of the diseases spread by contact dis- 
semination of the discharges from the upper respira- 
tory tract is, therefore, the major problem of modern 
epidemiology (the science of studying epidemics). 
Its solution can not be attained by any simple pro- 
cedure such as the pasteurization of milk or the 
drainage of mosquito breeding marshlands; but only 
by the far more diffseult task of detecting and isolat- 
ing human cases and carriers of disease. 


ISOLATION AND QUARANTINE 


The control of the contact-borne diseases by the 
appiication of intensive and scientific methods of iso- 


46 MAN AND THE MICROBE 


lation and quarantine is one of the most important 
and responsible functions of the health department of 
city or town; and the fulfilment of this function de- 
pends upon the whole-hearted and intelligent cooper- 
ation, not only of the medical profession, but of the 
general public as well. 

The first essential is, of course, that the health 
department should be notified of the existence of cases 
of communicable disease, which may prove a source 
of infection for others, at the earliest possible mo- 
ment. For this reason Sanitary Codes usually pro- 
vide that physicians, teachers, householders, and 
others shall report all cases of disease that are “pre- 
sumably communicable” without even waiting for a 
final diagnosis to be made. In many instances, as in 
diphtheria, typhoid fever, tuberculosis, and malaria, 
the Health Department laboratory can provide in- 
valuable assistance in establishing the diagnosis by 
special laboratory tests. 

As soon as a case of communicable disease is dis- 
covered it is the duty of the Health Department to 
establish isolation—that is, to see that the case is so 
cared for as to give every possible security against 
the transmission of the infective material. In all the 
more serious and acute diseases, such as diphtheria, 
typhoid fever, scarlet fever, measles, pneumonia, 
infant paralysis, and epidemic cerebrospinal menin- 
gitis, the room occupied by the patient must be main- 
tained as an isolated area, no one being permitted to 
enter it unnecessarily, and absolutely no one, except 
the doctor and the nurse or other attendant, being 
permitted to approach near to the patient or to touch 
anything in the room. The infected bodily discharges 
of the patient—in bed-pans, or on handkerchiefs as 
the case may be—and all objects and surfaces soiled 
with such discharges, such as bedding, eating utensils, 
and the like, should be disinfected according to rules 


THE CONTACT-BORNE DISEASES 47 


laid down by the Health Department. Nothing should 
leave the room until it has been thus disinfected, and, 
above all, the hands of the nurse or other attendant 
should be thoroughly washed with a disinfectant solu- 
tion before leaving the room or touching anything 
that is to be carried out of the room. Success in pre- 
venting the spread of communicable disease depends 
first and foremost upon such daily and hourly care, 
and it is upon the attendant upon the sick, whether 
nurse or relative, that the real responsibility must 
rest. Where such isolation as that described can not 
be secured in the home, it is the duty of the Health 
Officer to remove the case to a hospital where ade- 
quate care is possible. 

In the case of certain diseases, like mumps and 
whooping cough, in which the patient is not sick 
enough to be in bed, and against which grown people 
are generally more or less immune, such elaborate 
precautions are impracticable and unnecessary. In 
such diseases the Sanitary Code usually provides 
‘ merely that affected children shall remain out of 
school and be kept away from places of public assem- 
bly and, in general, from other children during the 
period of isolation. 

The length of time for which isolation need be 
continued varies in different diseases. Irrespective 
of any time limit, isolation must always be maintained 
until all active symptoms, such as discharging ears, 
have ceased. In whooping cough, however, the cough 
is an after effect which often persists long after the 
active disease process has ceased. It is most impor- 
tant that isolation regulations should be made as little 
burdensome as is consistent with safety. In diph- 
theria, cerebrospinal meningitis, and typhoid fever, 
the disappearance of the infecting organism can be 
established by laboratory tests. In the other common 
diseases we rely on an arbitrary time limit which 


48 MAN AND THE MICROBE 


experience has shown to be satisfactory. The stand- 
ard isolation periods are as follows: chicken-pox, 
until primary scabs have disappeared; German 
measles, eight days from onset; measles, seven days 
from onset; mumps, until glands have returned to 
normal size; infant paralysis, twenty-one days from 
onset; scarlet fever, twenty-eight days from onset; 
smallpox, until disappearance of all scabs and crusts; 
whooping cough, four weeks from onset or two weeks 
from first characteristic whoop. 

When the isolation period is over, the patient may 
be discharged and the room given a final thorough 
cleansing. Fumigation is unnecessary and useless 
except in the insect-borne diseases. If daily disin- 
fection has been carried on during the course of the 
disease the few germs which may have escaped im- 
mediate destruction will have died out with the lapse 
of time; and, if the isolation procedures have not 
been effectively practised, infection is already fairly 
certain to have spread to susceptible members of the 
family. , 

Quite as important as the care of the first case of. 
disease is the supervision of other members of the 
family, schoolmates, or associates, who have been in 
contact with the patient and may already have be- 
come infected by him before his condition was recog- 
nized. It happens, unfortunately, that many diseases, 
like measles and whooping cough, are particularly 
catching in the very early stages, so that it is too late 
when they are detected to prevent the transfer of 
infection to a second crop of cases. By careful super- 
vision of the contacts it is generally possible, how- 
ever, to prevent the transmission of disease to a third 
and still larger group; and this is one of the main 
objectives of modern epidemiology. 

The duty of the health officer is to exclude these 
contacts from school and places of assembly and to 


THE CONTACT-BORNE DISEASES 49 


keep them under observation until it is certain that 
they are not coming down with the disease. In some 
diseases, like diphtheria and epidemic cerebrospinal 
meningitis, we can discover by taking cultures 
whether a contact case is a carrier or not. In other 
instances the contacts should be quarantined for the 
incubation period of the disease—that is, the period 
which elapses between the time of infection and the 
first obvious signs of illness—unless they are known 
to be immune as the result of a previous attack. In 
cerebrospinal meningitis, this period is 2 to Io days; 
in chicken-pox, 14 to 21 days; in diphtheria, 2 to 5 
days; in German measles, 10. to 21 days; in measles, 
7 to 18 days; in mumps, 4 to 25 days; in poliomye- 
litis, 3 to 10 days; in scarlet fever, 2 to 7 days; in 
smallpox, I2 to 14 days; in typhoid fever, 7 to 23 
days, and in whooping cough up to fourteen days. 
Where a contact is known to be immune as a result 
of a previous attack the regulations need not gen- 
erally be enforced. The greatest care should be taken 
to watch contact cases which are in quarantine and 
to enforce isolation if any symptoms suggestive of 
communicable disease occur. 


THE SANITARY CONSCIENCE AND THE ASEPTIC 
SENSE 


In view of the fact that many of the common com- 
municable diseases, measles and whooping cough, for 
example, are particularly contagious in the very early 
stages before a real diagnosis is possible, it is of 
urgent importance to secure the intelligent coopera- 
tion of the general public in their control. In par- 
ticular school teachers and mothers of young children 
should be on the lookout for the symptoms generally 
associated with some infection such as coughing, 
sneezing, running nose or eyes, feverishness, head- 
ache, rashes of any kind, looseness of the bowels, or 


50 MAN AND THE MICROBE 


vomiting. Such symptoms may mean much or little; 
but whenever they appear children should be kept 
out of school and away from contact with their fel- 
lows and the doctor should be called if illness con- 
tinues. We need to develop what I have elsewhere 
called “the sanitary conscience,” a recognition of the 
serious responsibility which is incurred by exposing 
other people to infection with any communicable dis- 
ease, even the common cold. In the conduct of the 
important affairs of daily life it is sometimes neces- 
sary to take risks, but it is a sign of thoughtless folly 
rather than strength of will for people who are 
coming down with some disease to attend places of 
public assembly or pleasure parties. 

Above all, it is essential that infants and young 
children should be protected from exposure. The 
old saying, that a child must have these diseases 
sometime and the sooner they are over the better, is 
a dogma which has slain its thousands and its tens of 
thousands. ‘The fatality of measles and whooping 
cough is five times as great in infants under one year 
of age as in children over five; every month and 
every week for which infection can be postponed is 
so much gained in reducing the danger of a fatal 
result. 

For those who are well, the surest safeguard 
against communicable disease lies in the develop- 
ment of “the aseptic sense,’ an instinctive habit of 
keeping things that are not clean away from the 
mouth and nose and from the standpoint of bac- 
teriology everything that has not been specially 
cleansed must be regarded as a possible source of 
danger. It is an unpleasant truth that every time 
we come down with a cold it is because we have put 
the discharges from some one else’s mouth or nose 
into our own, and the actual carrying out of the fol- 
lowing two simple rules would probably do more than 


9% 


THE CONTACT-BORNE DISEASES § 51 


anything else for the prevention of communicable 
disease.” 

I. Nothing should ever go into the mouth except 
things to eat and drink and the toothbrush. Nothing 
he ever go to the nose except a clean handker- 
chief. 

II. The hands should be thoroughly washed before 
meals and before eating any food handled with the 
fingers. 


1See also ‘‘Personal Hygiene,” by A. J. McLaughlin, M.D., in 
the National Health Series. 


CHAPTER V 
THE ARTIFICIAL CONTROL OF IMMUNITY 


Vi1TAL RESISTANCE AND IMMUNITY 


ay the preceding chapters we have discussed the 
more important methods by which the entrance of 
disease germs into the human body may be prevented. 
When these primary defenses have failed there begins 
a second stage of the struggle, carried on within the 
body itself, and here, too, the science of bacteriology 
is able to intervene, and often in a complete and de- 
cisive fashion. 

The outcome of the battle between an invading 
germ and the defensive mechanism of the body is in 
part decided by the condition we term vital resistance. 
The factors included under this heading may be of 
widely different kinds. The fowl, for example, can 
not be inoculated with the disease called anthrax be- 
cause its normal body temperature is above the tem- 
perature at which the anthrax germ can grow; but 
Pasteur succeeded in giving fowls anthrax by chilling 
them in a bath of ice water. Krause and his asso- 
ciates have recently demonstrated that the course of 
tuberculosis in the rabbit and the guinea-pig is sub- 
stantially different and that this difference is due to 
the details of the anatomical structure of the lung in 
the two animals. Among human beings we are all 
familiar with the fact that vital resistance depends in 
large measure upon general vitality and that tuber- 
culosis and pneumonia are likely to develop (pro- 
vided the specific germs be present) if the vital 
resistance is weakened by exhaustion, underfeeding, 
or a previous attack of some other disease. 

52 


ARTIFICIAL CONTROL OF IMMUNITY 533 


Quite distinct from this sort of general vital re- 
sistance is the specific immunity which almost uni- 
versally follows an attack of some communicable 
disease. When a person recovers from almost any 
such infection he will have acquired an immunity 
which protects him against another attack, sometimes 
only for a few weeks but frequently for life. Such 
acquired immunity may be developed through attacks 
of disease so slight as to be scarcely noticeable or 
quite overlooked, and investigations, to which refer- 
ence will be made later on, have shown that a very 
large proportion of the population gradually acquires 
immunity against diseases like diphtheria and tuber- 
culosis through the occurrence of such very light 
attacks. When a new disease is introduced into an 
unprotected community, as when measles was brought 
to the Faroe Islands or when Indian and African 
troops in France during the war were exposed for 
the first time to tuberculosis, the rapidity and the 
fatality of the disease may be astounding. 

It is obvious that if we had some way of producing 
such specific immunity at will and without waiting 
for a natural attack to occur, in mild or in severe 
form, we should possess a most potent weapon in the 
war against disease. In a number of the com- 
municable diseases exactly this result has been ac- 
complished by the procedures of vaccine and serum 
treatment, and the number of diseases in which it can 
be attained is increasing year by year. 


SMALLPOX AND VACCINATION 


The first example of successful control of a com- 
municable disease through the creation of specific 
immunity was the practise of vaccination against 
smallpox introduced by Jenner a century and a 
quarter ago. It is difficult for us to realize the 
terrors of smallpox in the days before this discovery 


54 MAN AND THE MICROBE 


was made. Its ravages were almost universal, and 
about one person in every ten died of the disease. 
An English health officer of this period quaintly and 
correctly classified the citizens of his town by saying 
that so many had had smallpox, so many were at the 
moment having smallpox, and so many (the rest of 
the population) were still to have smallpox. As 
Macaulay says: 


“That disease over which science has since 
achieved a succession of glorious and beneficent vic- 
tories, was then the most terrible of all the ministers 
of death. The havoc of the plague had been far 
more rapid; but plague had visited our shores only 
once or twice within living memory; and the small- 
pox was always present, filling the churchyards with 
corpses, tormenting with constant fears all whom it 
had not yet stricken, leaving on those whose lives it 
spared the hideous traces of its power, turning the 
babe into a changeling at which the mother shud- 
dered, making the eyes and the cheeks of the be- 
trothed maiden objects of horror to the lover.” 


The practise of inoculation against smallpox which 
depended on the production of immunity by in- 
oculating the individual with the material from the 
pustules of a smallpox patient, had been in vogue in 
Asia for at least three centuries before the Christian 
era, and was finally introduced into England in 1718 
by Lady Mary Wortley Montagu, the brilliant wife 
of the British Ambassador at Constantinople. The 
reaction to this treatment was often severe and some- 
times fatal and it had little effect upon the general 
prevalence of the disease. That it should have been 
practised at all is striking evidence of the universal 
prevalence of smallpox and the horror which the dis- 
ease inspired. 

It was in 1796 that Edward Jenner gave us the 
modern practise of vaccination, which possessed all 


ARTIFICIAL CONTROL OF IMMUNITY 55 


the advantages of inoculation without its dangers. 
His discovery was made in the following way: In the 
rural district in which he lived many of the cattle 
were infected with a mild eruptive disease known as 
cowpox, and this disease was often contracted by the 
men and girls who milked the cows. There was a 
common belief that those who had had the cowpox 
were resistant against smallpox, and this theory Jen- 
ner tested out by vaccinating a boy, James Phipps, 
with cowpox material and then inoculating with true 
smallpox matter, in the fashion generally practised 
at the time for protection against natural smallpox. 
The cowpox vaccination “took”; the smallpox inocu- 
lation failed to “take,” showing that the vaccination 
had produced in the boy an effective immunity against 
the smallpox germ. During the years 1799-1801 
over 3000 different persons were thus vaccinated, and 
then inoculated, at the London Small-Pox Hospital 
with the demonstration of complete protection in 
every case. There is perhaps no other procedure in 
medicine which rests upon so ample and sure a basis 
of direct experimental evidence. 

Since Jenner’s day it has been shown that the 
inoculation of human smallpox material into the cow 
produces cowpox, and that by exposure to the body 
fluids of the cow the germ of smallpox has perma- 
nently lost its power to produce smallpox. Vaccine 
retains, however, the power to stimulate the human 
body so that it becomes immune against the virulent 
disease. The effect is not life-long or absolute. It 
wears off with the passage of time, so that vaccina- 
tion should be repeated about once in seven years. 
Yet even among those who have been vaccinated 
long before, the great majority resist infection and 
those who do contract the disease suffer in a rela- 
tively mild degree. Statistics for a group of Eng- 
lish towns showed, for example, a rate of 35 deaths 


56 MAN AND THE MICROBE 


per 100 cases among the unvaccinated, and only 5 
deaths per 100 cases among the vaccinated. 

A study of the general statistical results of the 
use of vaccination offers conclusive evidence in re- 
gard to the efficacy of the process. As soon as the 
practise of vaccination was introduced in the vari- 
ous countries of Europe, the terrible death rates of 
the nineteenth and preceding centuries ceased. In 
Sweden, the death rate for the twenty-eight years 
before vaccination was 2,050 per million, and for the 
forty years following vaccination 158 per million. 
The death rate in various countries corresponds to the 
prevalence of vaccination. Even as late as 1893-97 
the smallpox rate was over 9o per million in incom- 
pletely vaccinated countries like France, Belgium, and 
Austria, rising to 463 in Russia and 563 in Spain, 
while in well-vaccinated Germany and in the Scan- 
dinavian countries the rate has been I or less for the 
last half century. During the eight years before the 
American army entered Havana, and before vacci- 
nation was enforced, there were 3,132 deaths from 
smallpox in the city; during the next eight years 
there were seven. In 1905 and 1906 over three mil- 
kon vaccinations were performed in the Philippine 
Islands with the result that a toll of 40,000 deaths a 
year was changed to a few hundreds; the latter oc- 
curring in remote places which had not been reached 
with fresh and potent vaccine. In the provinces im- 
mediately adjacent to Manila there were 6,000 deaths 
a year from smallpox before vaccination and none 
after. When the health service of the Philippines 
was turned over to native officials in 1914, vaccina- 
tion was neglected, and as soon as enough susceptible 
children had been added to the population the disease 
broke out once more. In 1918 there were again 
50,000 deaths from smallpox in the Philippines, mine- 
tenths of them among the unvaccinated children. 


ARTIFICIAL CONTROL OF IMMUNITY 57 


There are unfortunately many communities in the 
United States which are heading straight for an ex- 
perience like that of the Philippine Islands through 
neglect of the safeguard of vaccination. In 1916 
there were 15,450 cases of smallpox with 48 deaths; 
in 1920 there were 94,691 cases with 366 deaths. We 
shall, no doubt, have some striking demonstration of 
the folly of neglect of vaccination during the next 
ten years; but any community which desires to do so 
can stamp out smallpox and keep it under control by 
the practise of vaccination and revaccination. 


THE SCIENTIFIC PRINCIPLES OF VACCINE 
TREATMENT 


Jenner’s discovery was purely an empirical one and 
limited to the particular disease with which he dealt. 
It remained unique for three-quarters of a century 
until Pasteur worked out the fundamental principles 
upon which the whole modern development of vaccine 
and serum treatment has been based. 

It was in connection with a disease of fowls, known 
as chicken cholera, that Pasteur made his first dis- 
coveries along this line. He had isolated the germ 
of this disease and proved that it could be produced 
at will by the inoculation with this germ of suscep- 
tible birds. On one occasion he used an old labora- 
tory culture for this purpose and found that it had 
become so weakened by long standing that the fowls 
no longer developed the typical disease; but when 
some of these same fowls were later inoculated with 
a fresh virulent culture they were found to have de- 
veloped an immunity against its attack. The fertile 
mind of Pasteur at once grasped the possible analogy 
between this phenomenon and that of Jennerian vac- 
cination. Was it possible, as a general method of 
controlling communicable disease, to prepare weak- 
ened or attenuated viruses which would be robbed of 


58 MAN AND THE MICROBE 


the power of harm but would retain the ability to 
stimulate the body so as to produce in it a state of 
immunity similar to that following an actual attack 
of disease? 

Pasteur’s next step was taken in connection with a 
disease of cattle known as splenic fever. After many 
eager and anxious months he succeeded in producing 
a vaccine for this disease, this time by exposing the 
germs to heat, a vaccine so effective that it would 
confer an almost complete immunity without harming 
the treated animals. On May 5, 1881, a public dem- 
onstration of this new procedure was given at the 
farm of Pouilly le Fort near Melun, as a result of 
the challenge of the skeptical editor of a veterinary 
paper. Twenty-five sheep and six cows were inocu- 
lated with the protective vaccine, and after a suitable 
interval these animals and a similar group of un- 
treated ones were inoculated with the virulent virus 
of splenic fever. The final inoculation took place on 
May 31, and altho Pasteur had boldly predicted, “The 
twenty-five unvaccinated sheep will all perish; the 
twenty-five vaccinated ones will survive,” he was a 
prey to intense anxiety when the crucial test came. 
On the morning of June 2, however, a telegram 
arrived from the once hostile veterinarian, announc- 
ing “stunning success,” and when Pasteur arrived 
at the farm in the afternoon amid the acclamation 
of the delegates from medical and veterinary and 
agricultural societies who crowded about the enclo- 
sure, twenty-two of the unvaccinated sheep were dead 
and two others were breathing their last, while the 
vaccinated animals were all in perfect health. 

By this demonstration, the broad principle was 
established that the production of immunity by the 
injection of weakened germs or killed germs or ex- 
tracts from dead germs is indeed a general and not 
an isolated phenomenon; and the way was opened 


ARTIFICIAL CONTROL OF IMMUNITY 59 


for one of the most brilliant chapters in the history 
of public health, a chapter which is still in the course 
of writing at the present day. 


Tue DEVELOPMENT OF VACCINE PROPHYLAXIS 


The first practical application of this new principle 
was made by Pasteur himself in the development of 
a vaccine for the treatment of rabies. In general, 
vaccines are used for the prevention rather than the 
cure of disease—that is, the vaccine is administered 
to well people whom we wish to protect against the 
danger of a future attack. The reason for this is 
that the immunity produced by a vaccine takes a con- 
siderable time to dévelop. Where an infection is 
localized in some special part of the body, as in the 
case of a carbuncle, for example, the use of a vaccine 
may aid in recovery by summoning up the resources 
of the rest of the body to repel the local attack. In 
the case of rabies there is another apparent exception 
to the general rule, since this vaccine is given to 
patients who have been bitten by a rabid animal. This 
is really, however, a preventive rather than a curative 
measure because it takes a long time (days or weeks) 
for the infective agent of rabies to find its way from 
the wound where it was introduced to the central 
nervous system where the disease is actually pro- 
duced ; and during this time the vaccine has an oppor- 
tunity to develop a condition of immunity. 

The vaccine for rabies is produced by drying the 
spinal cord of an animal inoculated with the disease, 
thus attenuating the germ which is present in the 
spinal tissues. First applied successfully by Pasteur 
in 1884, this vaccine reduced the fatality among per- 
sons bitten by a rabid animal from about ten per 
cent. to a fraction of one per cent., and its use at the 
Pasteur Institute in Paris alone has saved nearly 
3000 lives. 


60 MAN AND THE MICROBE 


A vaccine for cholera was prepared by Haffkine 
in India in 1895, and between 1896 and 1808, Pfeiffer 
and Kolle in Germany, Wright in South Africa, and 
Russell in the United States developed a highly effec- 
tive vaccine for the prevention of typhoid fever. 
This is prepared in a very simple fashion by heating 
a culture of typhoid bacilli to a point which will kill 
the germs without destroying their immunizing power 
and it is nowadays the practise to use a mixed vaccine 
which will protect against the two forms of para- 
typhoid fever as well, three doses of the mixed vac- 
cine rendering one immune against these two diseases 
and typhoid fever as well. By the application of 
waccine treatment the typhoid rate in the United 
States Army was reduced to one-tenth of its former 
figure between 1909 and 1914; and the freedom of 
the armies from this disease during the Great War 
was chiefly due to the use of this preventive. 

Active investigations are being carried on with the 
Gbject of preparing vaccines for other diseases with 
more or less significant success, and with much 
promise for the future. There is a good vaccine for 
plague; a vaccine which is extensively used, but of 
somewhat problematical value, for whooping cough; 
and Dreyer in England has a vaccine, for which he 
and his associates entertain high hopes, to be used in 
the treatment of tuberculosis. Perhaps the most 
hopeful line of research which is being actively 
prosecuted at present is that which leads to the 
preparation of vaccines for pneumonia. There are 
already vaccines which appear to be useful in deal- 
ing with certain forms of this disease, and Huntoon 
has recently prepared a new type of vaccine which 
may, perhaps, have a much wider field of usefulness. 

We have so far spoken only of the most charac- 
teristic form of immunity, that which is specifically 
related to a particular disease. It should be men- 


ARTIFICIAL CONTROL OF IMMUNITY 61 


tioned that the studies of the last five years have 
indicated that there is a certain degree of non-specific 
immunity produced by an attack of one communicable 
disease but effective to some extent against other 
types of infection. In general, among the drafted 
men who were collected in our army camps in 1917 
and 1918 the recruits from the cities showed a much 
higher resistance against communicable diseases in 
general than did those from the rural districts, largely, 
as is believed, on account of non-specific immunity 
due to greater exposure to various infections during 
the period of childhood. 


Tue Use oF IMMUNE SERA IN THE TREATMENT OF 
DISEASE 


Vaccines, as we have seen, are substances contain- 
ing principles derived from a disease germ, which 
when introduced into the human body stimulate the 
body cells to the production of a state of active im- 
munity. Such an active immunity is generally more 
or less permanent, but it takes time to become mani- 
fest. Therefore, vaccines are commonly used for the 
prevention of disease rather than for cure. 

If, however, we can vaccinate an animal against 
some disease, common to animals and men, and pro- 
duce in it a state of active immunity; if then we can 
withdraw some of the blood of the animal containing 
the immune principles, it should be possible to inject 
the animal blood serum containing such principles 
directly into the body of a patient suffering from the 
disease in question so as to neutralize the poison pro- 
duced by the invading germ and thus to faver re- 
covery by producing an immediate tho temporary 
passive immunity. This feat was first accomplished 
by Behring and Kitasato and their associates in 1890 
in the case of diphtheria and tetanus; and to-day we 


62 MAN AND THE MICROBE 


have a whole group of immune sera which can be 
used in this way. 

In the case of diphtheria, for example, the toxin, 
or specific poison, of the diphtheria bacillus is in- 
jected into the horse in gradually increasing doses, 
until the horse is able to sustain a dose several 
thousand times as great as that which would prove 
fatal to an untreated animal. During this period the 
tissues of the horse have been producing larger and 
larger amounts of diphtheria antitoxin (a substance 
which specifically neutralizes the toxin). The horse 
is then bled, and the clear blood serum, containing the 
antitoxin, is separated, purified, and standardized. Ili 
this antitoxic serum be used at a sufficiently early 
stage of the disease, recovery is practically certain; 
and the effect of its use has been to cut down the 
death rate from diphtheria in the general population 
to less than one-fourth of what it was before this 
treatment was available. 

We have to-day immune sera of proved effective- 
ness, not only for diphtheria and tetanus, but for 
plague, dysentery, epidemic cerebrospinal meningitis, 
certain forms of pneumonia, and yellow fever. The 
serum for cerebrospinal meningitis has cut down the 
fatality from this disease from seventy-five per cent. 
to twenty-five per cent. In the case of pneumonia 
we have to deal in reality with several different dis- 
eases, due to distinct types of bacteria but having 
symptoms more or less in common. For pneumonia 
caused by certain of these organisms we have sera 
which will substantially reduce mortality; for pneu- 
monia of other types we have as yet no such weapons 
at our disposal. 

Even in the case of diseases which are not common 
to man and the lower animals the principles of serum 
therapy may be applied by the treatment of one 
human case with immune blood derived from another 


ARTIFICIAL CONTROL OF IMMUNITY 63 


human case which has recently recovered from an 
attack. Such a procedure has been used with success 
in pneumonia, scarlet fever, measles, and mumps; 
and here, too, there is reason to hope for substantial 
new developments in the future. 


THe CHALLENGE OF DIPHTHERIA 


In connection with this general subject of vaccine 
prophylaxis and serum therapy the problem of diph- 
theria deserves special and more detailed considera- 
tion. In dealing with this disease we possess a more 
complete machinery of control than is available in 
the case of any other communicable malady. Much 
has been accomplished already in reducing th diph- 
theria death rate; but the important place which this 
disease still holds among the causes of mortality is 
a constant reproach to the medical and public health 
professions. 

In the first place, we can detect the carriers of 
the diphtheria bacillus with certainty by a simple 
bacteriological examination. In the second place we 
can determine whether a given individual is already 
immune against diphtheria or not by what is known 
as the Schick test. In this test a very minute amount 
of diphtheria toxin is injected into the skin, and if 
the person is immune no reaction occurs, while if he 
is not immune a characteristic reddened area de- 
velops. Thirdly, we can cure diphtheria when it has 
begun to develop, by the use of antitoxin; and, 
finally, we can protect those who have not yet be- 
come infected and are not already immune by the 
injection of a mixture of toxin and antitoxin which 
acts as a vaccine in stimulating the development of 
a state of active immunity against the disease. 

When a case of diphtheria occurs it is a simple 
matter to test all those who have been in contact with 
the case by bacteriological culture and by the Schick 


64 MAN AND THE MICROBE 


test. Those who are already immune and not carriers 
need no further attention. Those who are immune 
but have diphtheria bacilli in their throats should be 
isolated for the protection of others. Those who are 
susceptible but not carriers should be given toxin- 
antitoxin to protect them against possible future in- 
fection ; those who are carriers and susceptible should 
be isolated and given antitoxin, since they are in 
immediate danger. 

It is better policy to take measures to protect chil- 
dren against diphtheria without waiting till a case 
actually appears in their family or school room. In 
New York and many other cities campaigns have 
been carried out on an extensive scale for the Schick 
testing of the general school population in order to 
determine which children are already immune and to 
immunize those who are not, with the toxin-antitoxin 
mixture. These wholesale tests have brought out the 
very interesting fact that infants of three months or 
less generally possess a temporary immunity inherited 
from the mother. The proportion of immune infants 
drops from 85 per cent. during the first three months 
to only 30 per cent. in the second year as this in- 
herited immunity wears off. From this point the 
proportion of immune children gradually increases, 
in New York City up to 85 per cent. again after 
twenty years of age, no doubt as a result of slight 
unnoticed infections which often occur in crowded 
communities. In rural districts and in certain private 
schools where children are protected from chance 
exposures the proportion becoming immune will be 
very much less. The use of toxin-antitoxin for 
protecting non-immune school children has proved 
brilliantly successful. In Auburn, New York, for 
example, the number of days of school attendance 
lost as a result of diphtheria was 22,438 in 1921-22 


ARTIFICIAL CONTROL OF IMMUNITY 65 


and only 1189 in 1922-23 after a vigorous Schick 
testing and toxin-antitoxin campaign. It was esti- 
mated that the value of the educational time thus 
salvaged was over $10,000. 

The best of all methods of fighting diphtheria is to 
go back to a period long before the beginning of 
school life. Four-fifths of all deaths from diphtheria 
occur in children under five years of age so that we 
can not hope to accomplish very much without secur- 
ing the toxin-antitoxin treatment of children of the 
“runabout” age. Since children in the second year 
are rarely immune against diphtheria it is a waste 
of time in this case to use the Schick test. What we 
should do is to immunize all children about the time 
of their first birthday with the toxin-antitoxin mix- 
ture; and just so far as this is done will diphtheria 
cease to take its toll of over 12,000 lives a year in the 
United States. 


Tue PAST AND THE FUTURE 


We have now reviewed in general outline the chief 
problems involved in the control of the germ diseases 
and the weapons which are available for the conflict 
against our microbic foes. It remains only to con- 
sider the ground which has been already gained in 
the war against disease and the promise of further 

ictories in the future. 

The great plagues and pestilences which killed our 
forefathers by the thousands in the Middle Ages 
have been practically banished from the world. In 
civilized countries, typhus fever and bubonic plague 
and Asiatic cholera have become rare medical curi- 
osities. Even in the tropics yellow fever has been 
eliminated from all but a few isolated regions, and 
malaria and hookworm disease can be brought under 
control wherever the funds and the personnel are 


66 MAN AND THE MICROBE 


available for the conduct of the specific measures 
indicated for their eradication. 

Recent progress in the control of the more familiar 
infections which affect our own American communi- 
ties is clearly indicated by the table below, which 
indicates the change in the death rate from certain 
groups of diseases in the United States Registration 
Area during the past twenty years. 


Deaths per Per cent 
1,000 population Reduc- reduc- 
‘ ‘ 4 1900 1920 tion tion 
Tuberculosis, diphtheria, ty- 
phoid fever, and diarrhea... 4.1 pL Sa a 54 


Other communicable diseases 
(including particularly 


pneumonia and influenza).. 3.3 am 0.6 18 
All other diseases..0....... 10.1 8.4 I.7 17 
A OCALS Sate ttots abate oleta tr 17.5 13.0 4.5 26 


In the case of four communicable diseases, tuber- 
culosis, diphtheria, typhoid fever, and diarrhea, there 
has been effected a reduction of over 50 per cent. in 
the death rate during a period of two decades. The 
decrease of more than 2 per 1,000 in the case of this 
group of diseases means that every year two lives 
are saved for every thousand persons in the popula- 
tion or a saving of 200,000 lives in the United States 
each year. Here is a triumph for the forces of public 
heaith of which the generals of any victorious army 
might well feel proud. As the writer has elsewhere 
pointed out,” “If we had but the gift of second sight 
to transmute abstract figures into flesh and blood, so 
that as we walk along the street we could say, ‘That 
man would be dead of typhoid fever,’ “That woman 
would have succumbed to tuberculosis,’ “That rosy 
infant would be in its coffin,’ then only should we 

1 Winslow, C.-E. A. ‘The Evolution and Significance of the 


Modern Public Health Campaign.” Yale University Press, New 
Haven, 1923. 


ARTIFICIAL CONTROL OF IMMUNITY 67 


have a faint conception of the meaning of the silent 
victories of public health. For such achievements 
we may thank God and take courage for the future, 
bearing on our banners that eternal phrase of Cicero: 
‘In no single thing do men approach the Gods more 
nearly than in the giving of safety to mankind.’ ” 

The possibilities of the future are, however, quite 
as brilliant as those of the past. Half of the mor- 
tality from tuberculosis, typhoid fever, diphtheria, 
and diarrhea still remains to be eradicated. The 
other communicable diseases have yet to be effectively 
controlled; and there are vast possibilities of pre- 
vention among the diseases not directly due to the 
invasion of a hostile microbe. 

Dr. Dublin of the Metropolitan Life Insurance 
Company has recently pointed out that in the State 
of Massachusetts (for which the longest series of 
records are available) the average age at which men 
die has increased from less than 40 years in 1855 to 
more than 55 years in 1920, an addition of fifteen 
years to the span of human life; and Dr. Dublin esti- 
mates that by the application of well-proven methods 
the average age of our American population could 
be increased to nearly 65 years, adding ten years 
more to the figure now attained. 

Such are the past achievements and such the future 
possibilities of the public health campaign. The rate 
of its progress will depend only upon the financial 
and moral support which is given, on the one hand 
to the investigators who are constantly placing new 
weapons in our hands, and on the other to the admin- 
istrative health officials who are directing the actual 
use of those weapons. If we can realize that this 
war against disease is a very grim reality, costing 
our country hundreds of thousands of lives in the 
course of every year, and mobilize our forces with 


68 MAN AND THE MICROBE 


the same vigor we should display against a human 
foe, the victory will be assured, and we shall make 
rapid progress toward that happy condition foreseen 
by Pasteur in which the menace of microbic disease 
shall be lifted from the lives of men. 


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